Calves, being the replacement herd of a dairy farm, require efficient nutritional management which should not only improve their health and growth but also reduce the expenditure to be incurred by their rearing. Feeding young calves is a high cost of heifer rearing and therefore nutritionists are investigating the strategies that can reduce the charges of this phase. The nature and form of solid feed and its quantity consumed affects types of microbes and pace of rumen development [1
]. Typically, young calves are fed starter feeds high in grain to allow earlier development of rumen [2
]. However, free choice calf starter feeding during the preweaning period have been shown to lower rumen pH [1
], decrease ruminal motility, and cause hyperkeratinization, leading to rumen papillae clumping [4
The amount and type of roughage to be offered to the young calf are still unclear [2
]. To date, studies involving the use of roughages in calf diet have given variable results. The addition of forages to the diet has been found to result in lower DMI and weight gain, less β-hydroxybutyrate (BHBA) [5
], and consequently delayed rumen development [7
]. Other research has suggested that inclusion of dry roughage to the calf diet stimulates the muscular layer of the rumen [7
], promotes rumination [9
], and reduces ruminal plaque formation [11
One possible way to increase the DMI of forage-based starter is to reduce the particle size. Earlier work in calves by Coverdale et al. [12
] reported that 15% inclusion of consistent 8–19 mm particle size hay improved intake, ADG, and feed efficiency in calves. Similarly, Castells et al. [13
] reported that provision of free-choice chopped forage to milk-fed young calves resulted in higher feed intake and better performance without any negative impact on digestibility. Ackeren et al. [14
] documented that early feeding dry TMR containing 15% alfalfa hay and weaning at 8 weeks improved the weight gain at 15 weeks as compared to those fed component feeds.
Another way of improving the intake of forage-based diets in young calves could be the inclusion of chopped/ground fiber sources as a TMR. Greater intake, higher neutral detergent fiber (NDF)/acid detergent fiber (ADF) digestibility and a trend of higher gain to feed ratio was achieved in calves fed high fiber course mash TMR than those fed fine ground [15
] or pelleted TMR [16
]. On the other hand, higher weight gain was observed when TMR pellets consisting of finely ground straw and starter were fed until 8 weeks after weaning [17
]. Recently, Suarez-Mena et al. [18
] evaluated the use of low quality straw source with varying chop length. The study concluded that varying particles size of straw included at 5% had a minimal effect on ruminal fermentation indices, rumen pH, as well as rumen morphometry. Most recently, Kehoe et al. [19
] documented that calves can be fed on TMR containing 50% starter and 50% corn silage without any detrimental effects on ADG, health, and intestinal morphometry.
In adult cattle and sheep, forage particles >1.18 mm leaving the rumen is considered as a threshold [20
], and therefore can suffice as a stable rumen environment and provide a necessary abrasive factor for smoother papillae development [21
Inclusion of forages, in preweaned diets of young calves at >10% of the ration dry matter (DM) is not encouraged due to possible depression in the intake. However, recent work in small ruminants fattening showed that higher levels, up to 25% of finely ground straw at 2 mm in light fattening lamb, increased intake, growth performance, and reduced the incidence of acidosis [22
]. To date, limited published information is available on the comparative evaluation of conventional and pelleted TMR in milk-fed calves. Therefore, we hypothesized that straw-based pelleted TMR can reduce the weaning age through improved intake without affecting the growth performance of dairy calves. The objectives of this study were to determine the effects of physical form (conventional vs. pelleted) of complete feeds containing 15% fine ground OH on intake, weaning age, growth performance, blood metabolites, and rumen morphometry of dairy calves.
2. Materials and Methods
The experiment was approved by Animal Care and Use Committee (ACUC) (approval code for the submitted manuscript is DR/727 dated July 19-2017) the University of Veterinary and Animal Sciences (UVAS) Lahore and was carried out at Military Farm Renala, Okara Pakistan from May to August.
2.1. Experimental Design
Thirty newly born, crossbred (Frisian × Sahiwal) cow calves were blocked by sex and assigned to three dietary treatments with n
= 10 (five male and five female) calves in each treatment. Treatments were: (1) conventional calf starter (CCS) without hay (2) TMR containing 85% calf starter and 15% chopped OH with a chop length of 1.5 cm (3) pelleted TMR (PTMR) containing 85% calf starter and 15% OH. The hay was ground in a hammer mill so that it could pass through a sieve of 2 mm before uniformly mixing with grain starter for steam pelleting. Pellet size was 4 × 18 mm made at a temperature of 65–70 °C. All the experimental diets were isonitrogenous. Ingredient composition of treatments and their nutritive profile on DM basis is given at Table 1
2.2. Feeding, Weaning, and Husbandry
The duration of the experiment was 84 d. The calves were enrolled in study after ad libitum feeding of colostrum for 3 d. Calves were housed in individual steel pens (2.13 × 1.22 × 1.17 m) bedded with rubber mats. The pens were placed in two rows under a naturally ventilated open-sided shed. Electric overhead fans installed in the shed were used for cooling. During week 1, calves were fed whole milk, 4 L/d in two equal feedings at 0830 hours (h) and 1800 h. However, from week 2 to until the start of weaning, calves were fed 6 L/d, in two equal feedings. The milk offered to the calves was diverted from saleable production of the farm having at an average 11.9% total solids, 4.08% fat, and 2.89% protein. Calves were weaned off milk using the starter intake-based weaning (SIW) protocol described by De Passillé and Rushen [23
]. Briefly; daily milk allowances were adjusted on the basis of three-step targeted starter intake of 200, 600, and 800 g of starter intake for three consecutive days. At intermediate steps 1 and 2, milk allowance was reduced by 25% and fed twice daily. When the calf reached 50% reduction in milk allowance, milk feeding was carried out in the morning only. For all calves, the weaning was completed when individual calf starter intake reached to 800 g/d for three consecutive days. Milk feeding was carried out using steel buckets, and feeding utensils were washed using a sanitizer after every feeding. Calf starter and water were offered ad libitum individually in plastic buckets and measured on a daily basis.
2.3. Performance, Health, Sampling, and Analysis
Health parameters including fecal consistency, respiratory problems, and general appearance were recorded on daily basis on a scoring system from 1–5, 1 being normal and 5 being grave, as described by Heinrichs et al. [24
]. Animals with fecal score >3 and temperature >39.5 °C were treated according to farm protocols. Calves with scours were given oral rehydrant for three consecutive days or until the signs of sickness disappeared. Samples of starter and TMR feed were collected fortnightly, dried at 55 °C in a forced air oven and ground to 1 mm using a Willy mill. Samples were used to determine: DM contents (using hot air oven at 105 °C for 3 h), crude protein (CP) and crude fat [25
]. Samples were ashed by igniting the samples at 550 °C for 4 h in a muffle furnace. An α-amylase + sodium sulfite treated filtration methods were used for sequential determination of the NDF; whereas, an sulfuric acid + cetyltrimethylammonium bromide treated filtration methods were used for the determination of ADF) by using an Ankom 2000 fiber analyzer (Macedon, NY, USA) [25
Four male calves from each treatment were slaughtered with Islamic method in Butchery of Meat Science and Technology Department (UVAS, Lahore). After deskinning, rumen and reticulum were tied at pyloric and esophageal ends and removed by cutting between two knots. Similarly, remaining digestive and visceral organs were also taken out and weighed. Ruminal and intestinal contents were removed, organs washed with cold water, and reweighed. After visual examination rumen tissue samples were dissected as per procedures given by Lesmeister et al. [27
] and preserved in 30% formaldehyde solution for subsequent analysis. Morphometric analysis was carried out under Labomed Stereo Microscope using software Labomed Pixle pro.
2.5. Blood Sampling and Analysis
Weekly blood samples were collected, four h post morning feeding, using EDTA coated and non-EDTA vacutainers from jugular vein to harvest plasma and serum, respectively. Harvested plasma and serum samples were divided into aliquots and stored at −20 °C until further analysis. Plasma glucose and BUN were determined using colorimetric kits (catalogue # 11538: BioSystems; catalogue # 11537: BioSystems). Plasma BHBA concentration was measured using a colorimetric kit (Catalogue # H7587-58: POINTE SCIENTIFIC, INC).
2.6. Body Weight and Body Measurements
Body weight (BW) was measured at the start of experiment and then on a weekly basis using a digital weighing scale. Body measurements were carried out at the start and then on a weekly basis. Wither height (WH) was measured with measuring stick from base of fore foot to the highest point of the wither, heart girth (HG) was measured as a circumference by wrapping a tape around chest region just behind elbow, hip height (HH) was measured from base of the hind foot up to the hook bone and body length (BL) was measured as distance from point of shoulder to point of rump [28
2.7. Cost of Feeding
Cost of feeding per kg gain was calculated by dividing total amount expended on milk and starter feed consumed by total weight gained in kg by the calf at weaning.
2.8. Feed Efficiency (Entire Experiment)
Feed efficiency was calculated by dividing kg of weight gained by DMI in kg.
2.9. Temperature Humidity Index (THI) and Wind Velocity
The temperature and humidity were recorded twice daily by using TH meter. Height of the TH meter from ground was 2.5 m. The temperature humidity index was calculated using the formula [30
] given below;
THI = (0.8 × dry bulb temperature) + (% relative humidity/100) × (dry bulb temperature − 14.4) + 46.4
Wind velocity was measured daily at 1400 h by using smart sensor electronic anemometer (AR816; Guangdong, China).
2.10. Statistical Analysis
Data were analyzed as a randomized complete block design using mixed procedures of SAS [31
]. Initial body weight was used as a covariate for milk and starter intake, DMI, BW gain, ADG, and feed efficiency. Initial measurements were used as a covariate for analysis of final measurements and gain in WH, HG, HH, and BL. Starter DMI was used as a covariate for rumen development measures and organ weights. Effect of sex was analyzed as a fixed factor, found nonsignificant (P
> 0.05), and therefore removed from the model. Data measured over time was summarized weekly for individual calf and analyzed with repeated measures ANOVA. The model included fixed effects of treatment, week, and week × treatment interaction and calf as a random factor. Difference among means was considered significant at P
≤ 0.05 and trend reported at P
< 0.10. Mean values have been expressed as least square means. All the data were subjected to nonparametric SNK test to determine the normal distribution.