Pre-Weaning Performance and Genetic Efficiency Indices in Charolais and Limousine Calves Raised in Romania

Abstract

Understanding the genetic basis of growth and feed efficiency traits is essential for advancing beef cattle breeding programs. This study analyzed the average daily gain (ADG; from birth [day 0] to 200 days of age) and the Kleiber ratio (KR) in Charolais and Limousine calves raised in Romania. The data collection period was between 2020 and 2022. Genetic parameters were estimated using a maternal animal model based on 936 Charolais and 726 Limousine records sourced from the Romanian Breeding Association. For both traits, Charolais showed lower direct, maternal and total heritability estimates (0.44, 0.17 and 0.44 for ADG; 0.44, 0.17 and 0.44 for KR) compared to Limousine (0.67, 0.26 and 0.67 for ADG; 0.66, 0.26 and 0.67 for KR). The sex of calf and season of birth influenced the average daily gain and Kleiber ratio. Strong correlations were observed between the average daily gain and Kleiber ratio. The Kleiber ratio was confirmed as a reliable genetic indicator of feed efficiency across both breeds.

1. Introduction

The beef sector plays a crucial role in meeting the meat demands of the global population. The meat cattle production represented over 73% from total meat ruminant production in the period 2019–2023 according to FAOSTAT [1]. Improving feed efficiency in beef production is essential for ensuring both profitability and environmental sustainability within the industry. Feed efficiency is affected by various physiological and environmental factors. Charolais cows, in particular, demonstrate exceptional forage utilization, leading to a higher average daily gain (ADG) compared to other meat breeds. Specifically, the ADG from birth to weaning for Charolais calves was between 1.22 kg and 1.27 kg in Romania [2]. In the breeding program of the Limousine breed, a population of 2847 cattle was evaluated in the year 2025, and in the Charolaise breed a population of 5453 cattle was evaluated.

The main objectives of the breeding program for the Charolais breed included improving meat production traits. Specifically, birth weights for Charolais cattle in Romania should range between 42 and 45 kg, while weaning weights should be between 260 and 280 kg [2]. An essential goal was to enhance feed efficiency among beef breeds, aiming for maximum production with a high degree of feed conversion

In Romania, improving feed efficiency traits could significantly increase the profitability of beef farms. Nutrition plays a critical role in enhancing production and growth rates. To achieve high production levels, it is vital to provide adequate food in both quantity and quality, ensuring that the animals’ nutritional requirements are met for maintenance and growth.

Studies on the feed efficiency in beef breeds have been conducted in Romania, but the innovation of the present study was that it used genetic methods, selecting for improvement the traits of the ADG and Kleiber ratio (KR) in the Charolaise and Limousine breeds. The necessity of this research was for improving the meat production and feed efficiency in the Charolaise and Limousine breeds by selection based on the Kleiber ratio, via which the costs of the evaluation of beef cattle can be reduced. The selection of the cattle by breeding values for Kleiber ratio is important for the profitability of farms. The genetic parameters of ADG and KR are necessary in the breeding programs of the Charolaise and Limousine breeds. The study of feed efficiency in beef breeds has been realized by different authors in different countries by different methods, such as residual feed intake or KR [3,4,5].

Rational nutrition involves administering rations that support optimal production conditions. Feed digestibility is influenced by factors such as the breed, individual characteristics, age, production stage, physiological state, health and overall condition of the animal.

Animal genetics also play a crucial role in ensuring the sustainability of livestock through breeding programs that prioritize animal health and production improvement. The profitability of meat production is closely linked to expenses and income, with feed being a major cost in animal production systems [3]. In beef cattle production, feed costs account for approximately 70% of total operational expenses. Feed efficiency refers to the ability of cattle to convert feed into body weight gain, while metabolic efficiency indicates how effectively cattle utilize feed.

Beef cattle contribute significantly to a sustainable food system by consuming lower-value plant materials and byproducts, converting them into high-quality protein. A productive and environmentally efficient beef system is essential for food security. Calves from beef breeds are typically raised with their mothers until weaning at around 7 months of age. During the first three months, milk serves as the primary food source, supplemented with high-quality hay and concentrate feeds.

Due the cost of feed, feed efficiency is an objective in the breeding programs of beef breeds because it reduces the demand for global feed and assures environmental sustainability. The results of the present study contribute to a better understanding of the change in genetic parameters for feed efficiency in the function of breed, population and choosing a selection strategy, such as direct selection, to include feed efficiency in a breeding program.

Feed efficiency traits might be included in cattle breeding programs of the Charolaise and Limousine breeds raised in Romania. Genetic parameters are specific to each population, which is why it was necessary to estimate the genetic parameters for ADG and KR for Charolaise and Limousine populations raised in Romania. The production costs were lower when the selection of animals for feed efficiency was done using KR. For precise estimates of genetic parameters, using a maternal animal model was necessary to obtain accurate predictions of breeding value. In beef cattle, where it is difficult to measure the individual food intake in large herds, KR assures the selection of animals with high growth efficiency. Growth traits are influenced by maternal effects in different phases of growth. In the period from birth to weaning, maternal effects have a high influence on birth weight at weaning. In Romania, studies on the genetic parameters for KR from birth to 200 days were not realized until the present for the Charolais and Limousine breeds. The present study estimated the genetic parameters for KR in the Charolais and Limousine populations raised in Romania. This study has contributions in the selection and the genetic improvement of feeding efficiency in the Charolaise and Limousine breeds. KR was used for measuring feed efficiency without making measurements of individual intake. In the estimation of genetic parameters for growth traits, there are differences in the values of heritability in different phases of growth, which is why it is necessary to estimate the genetic parameters for ADG and KR to obtain accurate predictions of breeding value for feed efficiency of cattle.

In the estimation of genetic parameters for feed efficiency traits of Charolais and Limousine beef, different models were used without taking the maternal components into consideration. The studies comparing the genetic parameters of KR in the Limousine and Charolaise cattle breeds were few.

Models incorporating maternal genetic effects have been utilized by various authors to estimate genetic parameters for ADG and KR [4,5]. KR is the ADG/body weight^0.75. Enhancing ADG and the KR not only reduces feed costs but also improves the profitability and sustainability of beef cattle production [6]. For beef breeds, the phenotypes of calves are influenced by the ability of dams to assure a good nutritional environmental, the maternal animal model being adequate for genetic evaluation of the population for growth traits.

The objective of this study was to estimate the genetic parameters for ADG from birth to 200 days and the KR in Charolais and Limousine cattle populations using a maternal animal model for selection.

2. Materials and Methods

2.1. Animal and Experimental Procedure

The data used in this study were obtained from pre-existing databases based on routine animal recording procedures from the Romanian Beef Cattle Breeding Association. The data collection period was between 2020 and 2022.

The pedigree comprised a total of 1951 Charolais cattle, including 936 calves, 81 bulls and 934 cows. Each dam accounted for a minimum of one calf and a maximum of two, while sires accounted for a minimum of five calves and a maximum of 163. The 936 Charolais calves originated from 103 herds, with 781 females and 155 males born in 2021. During the summer, the calves from the Charolais breed were pastured, while in winter animals were housed in shelters. The calves were fed with milk ad libitum and hay concentrated feed.

For the Limousine breed, the pedigree included 1505 animals: 726 calves, 726 dams and 53 sires, specifically analyzing birth weight and weaning weight. These 726 calves originated from 54 herds, consisting of 350 females and 376 males. Each dam had one calf, while sires had a minimum of five calves and a maximum of 61. ADG was estimated from birth to weaning at 200 days.

The Limousine calves were born in 2020 and were raised on farms located across various counties in Romania. During the summer months, both calves and cows were pastured, while in winter, they were housed in shelters to ensure their comfort and well-being. Calves had unrestricted access to milk, which was collected at the farmer’s discretion. In addition to milk, the calves were also provided with concentrated feed and hay to promote healthy growth. Weighing took place at both birth and weaning to monitor their development.

2.2. Data Validation Protocol

The data validation protocol involved verifying that the ADG of the calves fell within acceptable limits. Grubbs’ test was employed to assess the validity of these values, ensuring the accuracy and reliability of the data collected.

$$\widehat{v}={\displaystyle \frac{X_{MIN/MAX}-\overline{X}}{\sigma }}$$

$$\widehat{v}=the tested value$$

(1)

$v_{\alpha ,n}$ = the critical value

If

$$\widehat{v}=the tested value<v_{\alpha ;n}$$

then the tested value (min/max) was not a foreign value in the data string, and the value was stored. If

$$\widehat{v}=the tested value>v_{\alpha ;n}$$

then the tested value (min/max) was a foreign value in the data string and was removed.

$$X=the value tested$$

$\overline{X}$ = the mean

$$\sigma =standard deviation$$

Student’s test was used for verification homogeneity of means.

$$t_{\overline{X1}-\overline{X2}}={\displaystyle \frac{\overline{X1}-\overline{X2}}{\sqrt{\frac{S_1^2}{n_1}+\frac{S_2^2}{n_2}}}}$$

(2)

where:

${\overline{X}}_1=$ the mean for group 1

$\overline{X_2}$ = the mean for group 2

$S_1^2$ = variance for group 1

$S_2^2$ = variance for group 2

$n_1$ = number of animals from group 1

$n_2$ = number of animals for group 2

The ADGs of the calves for Limousine and Charolais breed were within acceptable limits, and outlier values were not detected.

Differences between means for group comparison were tested statistically by the Fisher test.

The Fisher test was presented in the

Table 1. The Fisher test.

Variance Source	Degree of Freedom	Sum of Squares	Mean of Square	$\widehat{\mathit{F}}$
Between samples	DFI = s − 1	SSI = ∑C − CT	MSI = ${\displaystyle \frac{{SS}_I}{{DF}_I}}$	$\widehat{\mathrm{F}}={\displaystyle \frac{{MS}_I}{{MS}_i}}$
Inside the sample	DFi = N − s	SSi = ∑∑X2 − ∑C	MSI = ${\displaystyle \frac{{SS}_i}{{DF}_i}}$
Total	DFT = N − 1	SST = ∑∑X2 − CT	MST = ${\displaystyle \frac{{SS}_T}{T}}$

s = sample; N = total number of individuals; DF_I = degree of freedom between samples; DF_i = degree of freedom inside the sample; DF_T = total degree of freedom; SS_I = sum of squares between sample; SS_i = sum of squares inside the sample; SS_T = total sum of square; MS_I = mean of square between samples; MS_i = mean of square inside the sample; MS_T = total mean of square; $\widehat{F}$ = value of F_calculate.

.

$$F_{teoretic}=F_{DF for MS<}^{DF for MS>}$$

The Fisher test showed differences between means for group of calves from herds for an ADG 1.76 > 1.56, $\widehat{F}>F_{833}^{102},$(degree of freedom 102 for variance between herds and degree of freedom 833 for variance between calves in herd) in the Charolais breed. The feeding management methods from different herds influenced the ADG of calves.

The Fisher test showed differences between means for group of calves from herds for an ADG 8.52 > 1.56, $\widehat{F}>F_{672}^{53}$, (degree of freedom 53 for variance between herds and degree of freedom 672 for variance between calves in herd) in the Limousine breed.

2.3. Statistical Analysis

To estimate the genetic parameters, the restricted maximum likelihood method was utilized within a model that incorporated maternal genetic effects, focusing on a single trait. The fixed effects included sex and herd. The birth year was not considered because the maternal animal model was realized focusing on a single breed. The genetic parameters were estimated separately for the Limousine and Charolaise breeds. The calves from the Limousine breed were born all in the same year. The calves from the Charolais breed were also born all in the same year. Variance components estimation was conducted using a script [7] with a maternal animal model implemented in R version 3.5.1. The maternal animal model was [8]

y = Xb + Za + Wm + Spe + e

(3)

y = the vector of performances;

b = the vector of the fixed effects;

a = the vector of the random cattle effects;

m = the vector of the random maternal genetic effects;

pe = the vector of the permanent environmental effects;

e = the vector of the random residual effects.

X, Z, W and S were the incidence matrices referring to animal performance, the fixed effects, the direct effects, the maternal effects and the permanent environmental effects.

It was assumed that

$$var\left[\begin{array}{c}a\\ m\\ p\\ e\end{array}\right]=\left[\begin{array}{cccc}{\sigma }_a^{2}A& {\sigma }_{am}A& 0& 0\\ {\sigma }_{am}A& {\sigma }_m^{2}A& 0& 0\\ 0& 0& {I\sigma }_{pe}^2& 0\\ 0& 0& 0& {I\sigma }_e^2\end{array}\right]$$

(4)

where

A was the kinship matrix between cattle;

I was the identity matrix;

σ²_a was the additive genetic variance for the direct effects;

σ²_m, the additive genetic variance for the maternal effects;

σ_am, the additive genetic covariance between the direct and maternal effects;

σ²_pe was the variance due the permanent environmental effects;

σ²_e was the variance of the residual error.

According to the objective of this paper the following genetic parameters were estimated:

-

the direct heritability h_a² = σ²_a/σ_p², where σp² was the phenotypic variance;

-

the maternal heritability h_m² = σ²_m/σ_p²;

-

the covariance between direct and maternal effects as proportion of the phenotypic variance (σ_am/σ_p²);

-

the total heritability [9].

$$h_T^2={\displaystyle \frac{{\sigma }_a^2+0.5{\sigma }_m^2+1.5{\sigma }_{am}}{{\sigma }_p^2}}$$

(5)

where

h²_T was the total heritability and σ²_p was the phenotypic variance;

KR at 200 days was calculated with the following formula;

KR_i = ADG/BW^0.75 × 100;

ADG = average daily gain observed between the initial weight/birth weight and the weight at 200 days;

BW = the body weight at 200 days.

3. Results

Male calves had slightly lower birth weights (38.92 kg) than females (39.65 kg) in the Charolais breed but exhibited higher values for weight at 200 days, ADG, KR and metabolic weight (

Table 2. The descriptive statistics for growth traits in Charolais calves, including birth weight, weight at 200 days, average daily gain (ADG), Kleiber ratio (KR) and metabolic live weight.

Trait	Overall (Mean ± SE)	CV (%)	Females (Mean ± SE)	CV (%)	Males (Mean ± SE)	CV (%)
Birth weight (kg)	39.53 ± 0.19	15.03	39.65 ± 0.21	14.78	38.92 ± 0.51	16.21
Weight at 200 days (kg)	223.19 ± 1.03	14.11	222.33 ± 1.13	14.26	227.50 ± 13.22	13.22
ADG (kg/Day)	0.92 ± 0.01	17.23	0.91 ± 0.01	17.22	0.94 ± 0.012	17.06
KR (kg/kg0.75)	1.58 ± 0.01	7.87	1.57 ± 0.01	7.50	1.59 ± 0.012	9.45
Metabolic live weight at 200d (kg)	57.63 ± 0.20	10.72	57.46 ± 0.22	10.78	58.47 ± 0.48	10.29

).

Table 3. The descriptive statistics for growth traits in Limousine calves, including birth weight, weight at 200 days, average daily gain (ADG), Kleiber ratio (KR) and metabolic live weight.

Trait	Overall (Mean ± SE)	CV (%)	Females (Mean ± SE)	CV (%)	Males (Mean ± SE)	CV (%)
Birth weight (kg)	40.57 ± 0.14	9.08	39.82 ± 0.17	8.18	41.27 ± 0.20	9.49
Weight at 200 days (kg)	239.01 ± 1.43	16.06	226.15 ± 1.62	13.44	250.97 ± 2.12	16.40
ADG (kg/Day)	0.99 ± 0.01	19.25	0.93 ± 0.01	16.55	1.05 ± 0.011	19.50
KR (kg/kg0.75)	1.62 ± 0.01	7.44	1.59 ± 0.01	6.56	1.65 ± 0.13	7.70
Metabolic live weight at 200d (kg)	60.64 ± 0.27	12.01	58.22 ± 0.311	10.02	62.85 ± 0.40	12.36

presents the statistics for growth traits, ADG and KR for the Limousine cattle population.

Figure 1 illustrates the impact of birth season on ADG from birth to 200 days within the Charolais population and in the Limousine population. In the Charolais population, the distribution of calves by birth season was as follows: 27.67% were born in winter, 57.91% in spring and 14.42% in summer. Differences in means across the birth season groups were analyzed using the Fisher test, which indicated that the means differed significantly: 4.51 > 2.99 (p < 0.05) $\widehat{F}>F_{933}^2$ (degrees of freedom 2 for the variance between seasons and 933 for the variance between calves in season on ADG).

In our study, the distribution of calves in the Limousine population by birth season revealed that 10.05% were born in winter, 82.64% in spring and 7.31% in summer. Differences in means across the birth season groups were analyzed using the Fisher test, which indicated that the means differed very significantly (p < 0.001), 12.65 > 6.91$, \widehat{F}>F_{723}^2$ (degrees of freedom 2 for the variance between seasons and 723 for the variance between calves in season on ADG).

Table 4. Top 10 Charolais cattle ranked by highest estimated breeding values (EBVs) for growth traits including average daily gain (ADG), Kleiber ratio (KR) and weight at 200 days (W200d), with both direct and maternal components.

Rank	Direct ADG (kg/Day)	Maternal ADG (kg/Day)	Direct KR	Maternal KR	Direct W200d	Maternal W200d
1	0.32	0.17	0.21	0.11	60.57	40.88
2	0.28	0.16	0.19	0.11	53.13	37.06
3	0.28	0.15	0.19	0.11	52.35	36.5
4	0.27	0.14	0.18	0.10	51.56	31.82
5	0.26	0.12	0.17	0.10	51.19	29.49
6	0.26	0.12	0.16	0.09	47.15	28.92
7	0.24	0.12	0.16	0.09	45.71	27.26
8	0.24	0.11	0.15	0.09	43.76	27.14
9	0.23	0.11	0.15	0.08	41.43	26.58
10	0.19	0.11	0.15	0.08	38.94	25.01

presents the direct breeding values and maternal breeding values for ADG, KR and W200d in the Charolais population from birth to 200 days.

The breeding values provided insight into the genetic differences among animals regarding ADG and the KR from birth to 200 days. Breeding values for KR enabled the selection of cattle with higher efficiency, as this ratio served as a key indicator of an animal’s feed utilization. In the Charolais population, direct breeding values were found to be higher than maternal breeding values for both ADG and KR. Additionally, the direct and maternal breeding values for the top-performing cattle were greater for ADG compared to KR.

When selecting animals for ADG and KR, consideration could be given to both direct and maternal breeding values.

Table 5. Top 10 Limousine cattle ranked by highest estimated breeding values (EBVs) for growth traits including average daily gain (ADG), Kleiber ratio (KR) and weight at 200 days (W200d), with both direct and maternal components.

Rank	Direct ADG (kg/Day)	Maternal ADG kg/Day)	Direct KR	Maternal KR	Direct W200d	Maternal W200d
1	0.31	0.19	0.15	0.10	63.42	37.16
2	0.28	0.13	0.15	0.09	56.64	27.08
3	0.27	0.13	0.14	0.08	55.55	25.69
4	0.26	0.13	0.13	0.08	52.52	25.20
5	0.26	0.12	0.13	0.07	51.13	25.09
6	0.25	0.11	0.13	0.07	49.26	22.89
7	0.25	0.11	0.13	0.06	49.12	22.01
8	0.21	0.11	0.13	0.06	47.54	21.71
9	0.21	0.10	0.12	0.06	44.56	21.70
10	0.21	0.10	0.12	0.06	42.86	21.30

presents the direct and maternal breeding values for the top cattle in terms of ADG and KR within the Limousine population.

Similarly, in the Limousine population, the direct breeding values for cattle were higher than the maternal breeding values for both traits. Additionally, both direct and maternal breeding values were greater for ADG compared to KR.

Table 5 presents the breeding values for the top-performing cattle in terms of weight at 200 days.

Table 6. Estimated genetic parameters for average daily gain (ADG), Kleiber ratio (KR) and weight at 200 days (W200d) in Charolais cattle, including variances, heritability components and correlations.

Item *	ADG	KR	W200d
σ2a (Direct additive variance)	0.006	0.003	205.89
σ2m (Maternal genetic variance)	0.002	0.001	101.48
σam (Direct-maternal covariance)	−0.0007	−0.0004	−21.33
σ2pe (Permanent environmental variance)	0.005	0.003	603.34
σe2 (Residual variance)	0.0006	0.0004	15.88
σp2 (Phenotypic variance)	0.013	0.008	905.26
c2 (Proportion of σ2pe/σp2)	0.38	0.41	0.67
σam/σp2	−0.05	−0.05	−0.02
ha2 (Direct heritability)	0.44	0.44	0.23
hm2 (Maternal heritability)	0.17	0.17	0.11
ram (Genetic correlation)	−0.20	−0.20	−0.15
ht2(Total heritability)	0.44	0.44	0.25

* Variance components and heritability estimates.

displayed the variance and covariance components, along with the genetic parameters for ADG and KR W200d in the Charolais population.

The negative direct–maternal correlation could be negative because of genetic antagonism and because the dam–offspring covariance was negative.

In

Table 7. Estimated genetic parameters for average daily gain (ADG), Kleiber ratio (KR) and weight at 200 days (W200d) in Limousine cattle, including variances, heritability components and correlations.

Parameter	ADG	KR	W200d
σ2a (Direct additive variance)	0.01	0.005	448.05
σ2m (Maternal genetic variance)	0.004	0.002	174.64
σam (Direct-maternal covariance)	−0.0013	−0.0005	−54.68
σ2pe (Permanent environmental variance)	0.002	0.0008	743.89
σe2 (Residual variance)	0.005	0.0002	9.09
σp2 (Phenotypic variance)	0.02	0.01	1320.99
c2 (Proportion of σ2pe/σp2)	0.13	0.12	0.56
σam/σp2	0.08	0.07	−0.04
ha2 (Direct heritability)	0.67	0.66	0.34
hm2 (Maternal heritability)	0.26	0.26	0.13
ram (Genetic correlation)	−0.20	−0.20	−0.20
ht2(Total heritability)	0.67	0.67	0.34

, the genetic parameters for ADG and KR for the Limousine population are shown.

In the present study, c² was high, suggesting that maternal effects were due to maternal permanent environmental effects for weight at 200 days.

In

Table 8. Genetic correlations between Kleiber ratio and selected growth traits (direct and maternal breeding values) in Charolais and Limousine cattle.

Trait Pair	Breeding Value Type	Charolais	Limousine
200-day weight × KR	Direct	0.99	0.99
200-day weight × KR	Maternal	0.99	0.99
ADG × x KR	Direct	0.92	0.99
ADG × KR	Maternal	0.93	0.99

Average daily gain (ADG); Kleiber Ratio (KR).

, the genetic correlations between direct breeding values and maternal breeding values for weight at 200 days and KR are presented.

The genetic correlation between direct breeding values for ADG and KR was found to be very high in both the Charolais and Limousine populations.

4. Discussion

The coefficient of variability for the KR within the Charolais population was low, indicating a high level of homogeneity for this trait. The population also demonstrated uniformity in weight at 200 days and metabolic live weight at the same age, with minimal data spread, making the mean a reliable representation of the population. For birth weight, while the mean was sufficiently representative, the data spread was moderate. ADG from birth to weaning reflected both the calf’s growth potential and the dam’s ability to nurture the calf. Factors influencing ADG and KR include genetic elements such as breed, individual differences and sex, as well as environmental factors like nutrition and herd management practices. A calf’s maintenance norm represents the amount of nutrients required to sustain life without any change in body weight, while the production norm indicates the nutrients needed for each kilogram of weight gain. The quality of protein is a crucial factor in the growth of calves. Sex significantly influenced all growth traits, with males exhibiting higher ADG compared to females. Feed efficiency in calves refers to their ability to gain weight while consuming less feed, which helps reduce costs and ensures environmental sustainability. Achieving high production levels with effective feed conversion depends on genetic potential as well as the quantity and quality of feed provided. Nutrition plays a vital role in ensuring the health, growth and development of calves. A balanced diet is essential for increasing ADG, positively impacting calves’ vitality, growth intensity and overall body development. Rational nutrition focuses on administering feed aimed at achieving high a ADG. The ADG of calves during the pre-weaning period is largely influenced by the dam’s milk production, as milk constitutes a significant portion of the calves’ diet. Metabolic weight is a crucial factor in meeting the energy maintenance requirements of cattle. Maintenance energy is essential for sustaining vital bodily functions and supporting normal daily processes. The net energy needed for maintenance is directly proportional to the metabolic body weight of the cattle. At 200 days, the metabolic weight of Charolais and Limousine breeds was found to be very similar.

In the studied population, the birth weight of male calves was lower than that of females. However, males exhibited higher values than females for key metrics, including weight at 200 days, ADG, KR and metabolic live weight at 200 days. In the Charolais and Limousine populations, ADG was influenced by the gender of calf. In our study, males exhibited a higher ADG and KR compared to females in both the Charolais and Limousine populations; however, the differences in ADG were statistically significant when comparing males and females. Using the Student’s test showed that there was a very significant difference between means for ADG in the Limousine breed (p < 0.001), 8.82 > 3.29 and for Kleiber ratio 7 > 3.29 between the males and females. For the Charolaise breed, the difference between means for ADG for males and females was significant, t calc > t_∞;0.05, 2.09 > 1.96 (p < 0.05). For KR, there were not differences between means, t calc < t_∞;0.05, 1.58 < 1.96. The coefficients of variability for KR, birth weight and metabolic live weight at 200 days were low, indicating a high level of homogeneity within the Limousine population for these traits. In contrast, ADG had a sufficiently representative mean, although the data spread was moderate. Growth rates varied significantly, influenced by diet and heredity. Basal metabolism was generally higher in younger calves compared to mature cattle, and starting at two weeks of age, calves were provided with concentrated feed, high-quality hay and water at their discretion. The Limousine population exhibited higher mean values across all traits compared to the Charolais population. Additionally, the Limousine population had a greater number of males than females, whereas the Charolais population had the opposite. In the Limousine breed, the mean values for the studied traits were consistently higher for males compared to females. The results of the present study were similar to the results from other studies. In other studies, the gender differences for ADG from birth to weaning in the beef breed were observed as in the present study [10]. In the Aubrac beef breed, higher ADGs from birth to 6 months for males than females were reported [11]. The differences between the females and males can be explained by different hormone profiles that can affect their growth rates [11]. The gender differences could be due to different feeding practices. The different behaviors of males and females could influence the access to feed [11]. Notably, a higher mean for ADG at 210 days was reported in the Charolais breed at 0.990 kg, along with a KR of 1.60 [5], which surpassed the findings of our study.

Cattle with elevated KR values require lower maintenance from the weaning period onward, enabling them to achieve significant body growth without incurring increased maintenance costs [5]. The choice of the best cows on the basis of breeding values and use of the genetic parameters for KR in breeding programs of beef breeds could improve their profitability. Identifying cattle that could efficiently utilize feed resources is crucial for reducing feeding costs and enhancing feed efficiency [12].

In contrast, a lower mean for ADG during the pre-weaning period of 0.51 kg/day and a KR of 1.24 at 205 days were reported [4], which were less than the values observed in our study. Additionally, a KR of 0.02 in Charolais cattle in France at 15 months of age indicated that this ratio was age-dependent, typically decreasing as the calf matures [13].

Furthermore, a higher pre-weaning weight gain of 1.11 kg for Charolais beef was reported [14], which also exceeds our findings. Growth rates were influenced by breed and individual differences, while health status and environmental factors, such as climate, played significant roles in the level of feed intake among calves.

In beef breeds, the phenotype of calves regarding growth traits is influenced by the milk yield of cows, which is essential for ensuring an optimal nutritional level. This ability is largely determined by genetic factors [7]. In maternal populations, it has been recommended to select based on the combined direct breeding value and maternal breeding value [7].

The breeding values provided insight into the genetic differences among animals regarding ADG and the KR from birth to 200 days. Breeding values for KR enabled the selection of cattle with higher efficiency, as this ratio served as a key indicator of an animal’s feed utilization. In the Charolais population, direct breeding values were found to be higher than maternal breeding values for both ADG and KR. Additionally, the direct and maternal breeding values for the top-performing cattle were greater for ADG compared to KR. When selecting animals for ADG and KR, consideration could be given to both direct and maternal breeding values. Table 4 presents the direct and maternal breeding values for the top cattle in terms of ADG, KR and W200d within the Limousine population.

Maternal permanent environmental effects were found to be greater for ADG and KR, indicating that these traits were significantly influenced by the dam’s environment from birth to weaning. In the present study, c² was moderate, suggesting that maternal effects were due to maternal permanent environmental variance. Direct heritability for both ADG and KR was higher than maternal heritability for these traits. The value of heritability from our study in the Charolaise population could be influenced by environmental conditions in which this population was evaluated because each change in the environmental conditions changed the percentages of these in total variance, inclusive pf additive variance. Variable environmental conditions reduced the value of heritability and uniform environmental conditions increased the heritability. The direct, maternal and total heritability in the Charolais population was lower than in the Limousine breed because the environmental conditions were more variable, the number of herds where the environmental conditions were more uniform being greater in than in the Limousine population, where the number of farms was lower than in Charolais population. The feed management in farms could be different. Additionally, the correlation between direct and maternal genetic effects was negative for both traits. In our study, the direct, maternal and total heritability estimates for ADG and KR were all notably high, with values for these three types of heritability being very similar for both traits. The negative correlation between additive direct and maternal effects reflected the structure of data records and could be influenced by a negative dam–offspring environmental correlation. Other reasons could be additional variation between sire lines, genetic material being imported and sire x year interaction. The direct and total heritability was high in the Limousine population, suggesting that the environmental conditions were uniform. In our study, c² was low, suggesting that maternal effects were due to maternal genetic effects in the Limousine breed. The genetic correlation between direct breeding values for weight at 200 days and KR was found to be very high, indicating a strong relationship with ADG from birth to 200 days in both the Charolais and Limousine populations. Additionally, the genetic correlation between maternal breeding values for ADG and KR was also notably high. This strong correlation highlighted the close relationship between ADG from birth to 200 days and KR. Additionally, the genetic correlation between maternal breeding values for ADG and KR was also notably high, further emphasizing the interconnectedness of these traits. The similarities of heritability values from our study with the heritability from other studies were observed, as direct heritability for the Kleiber ratio at 210 days, reported at 0.40, and higher maternal heritability of 0.20 in the Charolais breed were observed in previous studies [5]. Moderate heritability estimates of 0.31 have been documented across various beef breeds [15]. Differences between results from our study for heritability and those of other studies were observed. Additionally, moderate heritability values of 0.34 for ADG and 0.31 for the KR at 15 months were reported [12]. In contrast, a higher heritability estimate of 0.52 for the KR was found in the Bonsmara beef breed [16]. In another study, lower direct heritability for ADG was reported at 0.19, with a KR heritability of just 0.14 [6], both of which were lower than the values obtained in our study. Other research indicated heritability for ADG from birth to 205 days at 0.21 [4] and heritability for the KR at 0.28 [12]. Moreover, moderate heritability for the KR from birth to 205 days was reported at 0.22 in a Hereford herd [17], while direct heritability for pre-weaning ADG was documented at 0.22, with maternal heritability at 0.18 in the Charolais breed [14]. In our study, we found negative direct–maternal correlations for both traits. In other studies, it was reported that the KR was strongly correlated with ADG [12,18]. Animals exhibiting good feeding efficiency contributed to reduced gas emissions per unit of weight produced, primarily due to decreased daily food consumption [19]. Therefore, incorporating KR into breeding programs for beef cattle was essential [20]. A direct heritability estimate of 0.43 for pre-weaning KR, similar to our findings, was obtained in a multibreed beef cattle study [21]. Higher heritability values for ADG (0.55) and the KR (0.53) were reported in the Fogera breed [22]. Reducing feed input per unit of production could enhance herd profitability by 9% to 33% [23].

Feed efficiency varies among cattle and could be improved through the selection of animals that demonstrate the highest feed efficiency [24]. Growth rates are influenced by breed and individual characteristics, while health status and climate conditions also significantly impact feed intake levels among calves [25]. During the suckling period, one study found no significant differences in weight gains between male and female calves [26].

To achieve a higher ADG, it was essential to provide cattle with a comfortable environment and ensure high-quality feeding. The milk yield of beef cows played a critical role in the ADG of calves [27]. Notably, milk production varied among beef breeds, with the Charolais breed typically producing more milk than the Limousine breed.

Additionally, milk yield was influenced by seasonal factors, increasing when cows were pastured in the spring. The analysis of calf distribution by birth season in the Charolais population revealed a significant prevalence of births in spring, followed by summer and autumn. The results of the Fisher test demonstrated that the mean weights of calves varied significantly across these birth seasons (p < 0.05). This highlights the impact of seasonal factors on calf growth and performance, suggesting that management strategies could need to be adapted based on the timing of births to optimize calf health and productivity. Understanding these seasonal influences was essential for improving breeding and management practices within the Charolais population. The distribution of calves in the Limousine population showed a pronounced concentration of births in spring, with a minimal proportion born in winter and summer. The analysis using the Fisher test revealed that the mean weights across these birth seasons differed very significantly (p < 0.1%). This finding underscored the critical influence of birth season on calf growth and performance, suggesting that management practices should be tailored to account for seasonal variations in calf production. Recognizing these patterns is vital for enhancing the overall productivity and health of the Limousine population. Similarities of results from the present study with results from other studies were observed for the influence of season on ADG. The season of birth significantly affected ADG of calves, as one study indicated that birth season had a substantial impact on the 205-day weight of calves [28].

Farm management practices could also influence the ADG achieved by calves. Improvements in calf performance could be realized through adjustments in nutrition and enhanced genetic selection efficiency [29].

The mean metabolizable energy requirement for the maintenance of growing cattle is approximately 0.672 MJ/kg^0.75 [30]. The high heritability estimates for ADG and the KR in our study suggest that significant genetic progress could be made in both Charolais and Limousine cattle populations. KR could serve as a valuable tool for selecting cattle based on growth efficiency.

Both the Charolais and Limousine breeds demonstrated high ADG and KR from birth to 200 days. The direct, maternal and total heritability for these traits were notably higher in both breeds. Additionally, the genetic correlation between direct breeding values and maternal breeding values for ADG and KR was very strong.

ADG from birth to weaning was influenced by both the calf’s genetic growth potential and the dam’s nurturing ability. Various factors, including genetic traits (such as breed and individual differences), sex and environmental conditions (such as nutrition and herd management), played significant roles in shaping these outcomes. Understanding these influences is essential for improving growth performance and efficiency in the Charolais and Limousine populations.

Nutrition is crucial for the health, growth and development of calves. A balanced diet is fundamental for enhancing ADG, which in turn positively affects calves’ vitality, growth intensity and overall body development. Implementing rational nutrition strategies that prioritize feed aimed at maximizing ADG is essential.

Furthermore, the ADG of calves during the pre-weaning period is significantly influenced by the dam’s milk production, highlighting the importance of maternal nutrition in shaping calf performance. Ensuring optimal nutrition for both dams and calves is therefore vital for improving growth outcomes and overall herd productivity.

The net energy required for maintenance is directly proportional to the metabolic body weight, underscoring the importance of this metric in assessing cattle health and performance. Notably, at 200 days, the metabolic weights of both the Charolais and Limousine breeds were found to be very similar, indicating a comparable energy maintenance need between these two breeds. This similarity suggested that management practices aimed at optimizing energy intake could be effectively applied across both breeds to ensure their health and productivity.

The analysis of the studied population revealed that while male calves had lower birth weights compared to females, they demonstrated superior performance in key growth metrics such as weight at 200 days, ADG, KR and metabolic live weight at the same age. This indicated that despite a lower birth weight, male calves were able to achieve greater growth efficiency and overall development. Understanding these differences is crucial for optimizing management practices and breeding strategies to enhance the productivity of both male and female calves in beef production systems.

The findings indicated that maternal permanent environmental effects played a significant role in shaping both ADG and KR in calves. The greater influence of the dam’s environment from birth to weaning highlighted the importance of maternal care and conditions in determining these traits. This underscores the need for focused management practices that enhance the maternal environment to improve the growth performance and efficiency of calves, ultimately contributing to better outcomes in beef production.

For improving ADG and KR, feeding management strategies can be adjusted according to the birth season and sex of calves. Feeding practices could be different for males and females, with different diets or different amounts of feeds for increasing ADG. The choice of the best environment and management systems for the Charolaise and Limousine breeds could improve ADG and KR. Conducting breeding programs by the selection of the best animals could improve the weight at birth, weight at weaning and, implicitly, the gain.

Cattle exhibiting the best direct and maternal breeding values for ADG and KR will be selected for reproduction, aiming to enhance these traits within the Charolais and Limousine populations.

5. Conclusions

Charolais and Limousine populations raised in Romania had high ADG and KR from birth to 200 days. The direct, maternal and total heritability for ADG and KR was high in the Charolaise and Limousine populations. The genetic correlation between the direct breeding values of cattle and maternal breeding values for ADG and KR was very high. The KR is an important trait which is necessary to include in the breeding programs for both Charolaise and Limousine populations raised in Romania for genetic evaluation for feed efficiency. The cattle with the best direct and maternal breeding values for ADG and KR will be selected for reproduction for improving these traits in the populations of the Charolais and Limousine cattle breeds. The genetic evaluation for feed efficiency with KR of Charolais and Limousine populations reduces the costs for production in farms.