Optimising Sheep Diets for Sustainability: Corn or Barley with Alfalfa?

Abstract

Forages like alfalfa haylage (AH), which are high in crude protein (CP), require energy-rich supplements to optimise nutrient intake, improve digestibility, and enhance nitrogen use efficiency thereby promoting sustainability in livestock production. The objective of the study was to determine whether corn or barley serves as better supplement to AH for achieving these goals. A feeding trial was conducted as an incomplete change-over design with four treatments, four periods, and four animals per period. The concentrate was fed at a rate of 30 g kg⁻¹ M^0.75 wether sheep d⁻¹ and consisted of: (i) 100% corn (CG), (ii) 67% corn and 33% barley (CG67), (iii) 33% corn and 67% barley (BG67), and (iv) 100% barley (BG). CG67 showed lower dry matter intake (DMI) (p < 0.001) but higher dry matter (DM) digestibility (p < 0.01). BG had the highest intake of neutral detergent fibre (NDF) (p < 0.01), CP (p < 0.001), and CP digestibility (p < 0.001). Both BG and BG67 exhibited higher N balance than CG and CG67 (p < 0.001). The results suggest that, given the quality of AH and the concentrate level of 30 g kg⁻¹ M^0.75 used in this study, supplementing barley to an AH-based diet is more beneficial for enhancing sustainability in sheep nutrition than supplementing corn.

1. Introduction

Sustainable feeding systems aim to enhance nutrient intake, improve nitrogen balance, and reduce overall emissions. Forages high in crude protein (CP), such as alfalfa haylage (AH), require energy-rich supplement feedstuffs to optimise nutrient intake, improve ration digestibility, and maximise nitrogen use efficiency as key components of sustainable livestock production [1]. A more synchronised release of energy and nitrogen promotes the synthesis of microbial proteins and fatty acids in the rumen [2,3]. This, in turn, enhances microbial nutrient assimilation [4], subsequently increases ration intake, digestibility and N utilisation [5,6,7,8].

Both dried corn grains (corn) and barley grains (barley) serve as effective energy supplements for ruminants. Compared to barley, corn contains at least 15% more starch (5–10% more energy), but has about 3% less CP. When ground or dry-rolled, corn can be a better source of energy than barley in forage-based diets [9,10,11]. In contrast, the feeding value of barley remains constant regardless of processing [12]. The reason is that the starch in the vitreous endosperm region of corn is surrounded by zein, which is resistant to microbial invasion and is only 55 to 70% digested in the rumen [13]. Barley, however, contains highly digestible protein and easily accessible starch, resulting in a faster fermentation rate, with ruminal starch digestibility often exceeding 90% [14] and sometimes reaching 98% [15]. Consequently, the overall digestibility of corn is lower than that of barley, which can reduce microbial protein synthesis when corn is added to protein-rich forages. Conversely, completely replacing corn with barley has been reported to negatively affect lamb growth performance [16,17], while no significant differences in dry matter intake (DMI) were observed in beef cattle fed high-concentrate corn or barley diets [18]. Some research suggests that partially replacing corn with barley in cereal mixtures with differing fermentation rates [4,19] can improve growth performance in lambs [17], heifers [20] and milk production in dairy cows [21,22]. However, intake and digestibility results vary due to differences in the supplementation rate, animal type, and forage quality [11,23]. Despite existing research, limited data are available on how partial replacement of corn with barley in AH-based diets influences nutrient intake, digestibility, and nitrogen utilisation in sheep. Most prior studies have focused on high-concentrate or total mixed rations, with less emphasis on forage-rich diets containing highly soluble protein sources like AH.

We hypothesise that partially replacing corn with barley in AH-based diets will enhance synchrony between energy and nitrogen release in the rumen, leading to improved microbial protein synthesis, greater nutrient digestibility, and enhanced nitrogen use efficiency compared to diets containing corn alone. This study aims to evaluate the effects of replacing corn with barley on nutrient intake, digestibility, and nitrogen utilisation in sheep fed AH-based diets. The findings are expected to inform strategies for improving nutrient synchrony and promoting sustainable feeding practices in forage-rich systems.

2. Materials and Methods

2.1. Alfalfa Haylage

The first cut of alfalfa was harvested at the beginning of flowering (when 30–40% of the crop was in full bloom). The crop was wilted for at least 24 h to achieve a dry matter (DM) content of approximately 500–600 g kg⁻¹ of fresh weight. The wilted forage was baled without additives using a John Deere round baler (bale diameter: 1.2 m) and then wrapped with 4–6 layers of white plastic film using a Pöttinger bale wrapping machine. The DM content of 500–600 g kg⁻¹ is too low to ensure safe storage; the bales were wrapped in plastic film to allow for anaerobic fermentation and preserved as haylage. The term “haylage” is used because the physical characteristics and DM content are closer to hay than to traditional silage, while the forage is still preserved through fermentation. This intermediate moisture level requires careful baling and wrapping to maintain anaerobic conditions and is particularly common in systems where wilting capacity is high or where silos are not used [24]. The name “haylage” therefore reflects both the preservation method and the moisture content, bridging the properties of hay and silage.

The plastic-wrapped bales were transported to the Grassland Research Centre of the University of Zagreb, where they were stored for at least 60 days before use. A total of six bales of alfalfa haylage (AH) were selected for this study.

Before the start of each trial period, the AH was chopped to a particle length of 3–5 cm using a commercial chopper and compressed by hand into plastic bags (20 L capacity each). The reason is that in big bale technology, forage is typically cut to longer lengths which together with the higher DM content helps the bales to retain their shape. However, chopping the haylage to shorter lengths before bagging and further feeding improves in-bag compaction and more importantly prevents selective feeding by sheep—specifically, the tendency to eat leaves and avoid stems.

The bags for an approximately 10-day feeding period were sealed with plastic film and stored in a cold chamber at 4 °C to prevent spoilage. The daily AH ration for each animal was weighed in a plastic bag on the day of feeding.

2.2. Concentrate

Corn grains (corn) and barley grains (barley) were produced using standard agricultural practices, dried at approximately 40 °C to a dry matter (DM) content of 87–88%, and stored separately in 50-litre plastic containers at room temperature until used for the experiment. The concentrates (corn, barley, and their mixtures) were weighed daily into plastic bags and offered separately from the alfalfa haylage (AH) to ensure complete consumption and avoid feed refusals.

The animals were fed twice daily, with approximately half of the ration provided at 9:00 a.m. and the other half at 4:00 p.m. No other feed was offered besides the AH and the concentrate. Fresh, clean water was available ad libitum throughout the experimental period.

2.3. Dietary Treatments

The concentrate was fed to the animals at a rate of 30 g kg⁻¹ M^0.75 day⁻¹, resulting in individual intakes ranging from approximately 555.6 g to 635.1 g day⁻¹.

The trial included four feeding treatments in which alfalfa haylage (AH) was supplemented with:

(i)

100% corn (treatment CG);

(ii)

67% corn and 33% barley (treatment CG67);

(iii)

33% corn and 67% barley (treatment BG67);

(iv)

100% barley (treatment BG).

The four treatments were randomly assigned to the four sheep in each period. Each feeding treatment was replicated four times over the four experimental periods.

2.4. Animals

Suffolk wether sheep were used in this study. The animals were approximately 2 years old, with body weights (BW) ranging from 49 to 56 kg (mean: 54 kg; standard deviation: 5.0 kg). Prior to the experiment, the sheep were dewormed, given a health check, and had the fleece trimmed around the tail. They were exposed to natural or artificial light daily from 8:00 a.m. to 8:00 p.m.

Body weight was measured twice during each experimental period using a Trutest scale: once before the adaptation phase and again before the start of the intake, in vivo digestibility, and nitrogen and water balance measurements. The amount of concentrate provided was adjusted individually for each animal based on its BW.

2.5. Adaptation to the Feeding Treatment

The animals were housed individually in pens (1.5 × 2.2 m) during a 12-day adaptation period prior to each of the four feeding treatments. This adaptation phase served as a reset period, allowing the animals to adjust to the new treatment. Their movement was limited, but they could lie down comfortably. Sawdust was used as bedding. Each pen was equipped with individual feeders and drinkers, which were cleaned daily. The feeders were designed to separate the bulky forage from the concentrate.

2.6. Determination of Ad Libitum Intake, In Vivo Digestibility and Nitrogen Balance

After the animals were adapted to the feeding treatments, they were fitted with faecal collection bags and housed individually in cages measuring 1.36 m × 1.53 m × 1.49 m. Each cage was equipped with individual feeders and drinkers, which were cleaned daily. The cage floor was made of perforated hard plastic with openings designed to prevent paw injuries. Beneath the floor, an inclined metal surface directed excreted urine into a plastic collection container (40 cm × 20 cm × 30 cm).

During the measurement period, animals were offered AH ad libitum for the first 4 days. For the following 7 days, the AH offered was restricted to 10–15% above the amount of AH consumed the previous day. Water intake, AH refusals, faeces, and urine output were recorded each morning before feeding.

2.7. Samples for Chemical Analysis

Corn and barley samples were collected before each study period (approximately 1.5 kg each) and stored at room temperature until chemical analysis. AH samples were collected daily, during the 11-day measurement period, at approximately 100 g day⁻¹, while weighing the relative daily AH amount, and stored in plastic bags. The samples of AH residues were taken daily before the morning feeding. Additionally, the faecal and urine samples were collected daily, gathering 10% of the excreted faeces and urine. To preserve the daily excreted urine, 100 mL of 2 mol/L sulfuric acid was added to the urine collection container to achieve a pH of 2–3. All samples of fed AH, AH residues, faeces, and urine were stored at 4 °C until the end of each experimental period. Afterward, the samples were transferred to −20 °C storage before conducting chemical analysis.

2.8. Determination of In Vivo Digestibility and N-Balance

The digestibility of DM, crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and starch was calculated using the equations [25]: DMD = (DM intake − faecal DM excreted)/DM intake; starch digestibility = (starch intake − starch faecally excreted)/starch intake; NDF digestibility = (NDF intake − NDF faecally excreted)/NDF intake; ADF digestibility = (ADF intake − ADF faecally excreted)/ADF intake; CP digestibility = (CP intake − CP faecally excreted)/CP intake.

Nitrogen balance was calculated by subtracting the amount of nitrogen excreted in faeces and urine from the amount of nitrogen ingested. The water balance was calculated by subtracting the amount of water excreted in urine and faeces from the total water intake (AH, concentrate and water).

The experiment was conducted in accordance with the Ethical Guidelines for the Use of Animals in Research and the Council Directive of the European Economic Community (EEC) (1986). The study was approved by the Ethics Committee for Scientific Research of the University of Zagreb Faculty of Agriculture, Croatia (Ethical reference number: 380-71-01-06-1).

2.9. Chemical Analyzes

The DM content was determined by drying the samples for 48 h in a fan dryer (ELE International) at a temperature of 60 °C to a constant sample weight. The organic matter (OM) content was determined by burning the samples in a microwave oven (Milestone PIYRO, Italy) at a temperature of 550 °C for 3 h.

Nitrogen content was determined using the Kjeldahl method [26] and CP content was determined by multiplying the N content by a factor of 6.25. The NDF and ADF content was determined using the Ankom filter bag technique [27]. The pH value was determined using the pH meter 315i (WTW). The content of volatile fatty acids was determined using a gas chromatograph and a liquid–liquid extraction with two different solvents (dichloromethane and methyl tert-butyl ether) [28]. The lactic acid content was determined enzymatically using the Express Auto biochemical analyser. Starch was analysed enzymatically [29] by first gelatinising samples with α-amylase, followed by amyloglucosidase digestion to convert dextrins into glucose. Glucose was quantified using a colorimetric assay (e.g., glucose oxidase-peroxidase), and starch content was calculated by multiplying glucose concentration by 0.9. Analyses were performed in duplicate and expressed on a dry matter basis. This method is widely accepted for its specificity in distinguishing starch from other polysaccharides.

2.10. Statistical Analyses

Descriptive statistics for means of four measurements and standard deviation were calculated for the parameters investigated. The experiment was statistically analysed as an incomplete change over design with 4 treatments, 4 animals and 4 time periods, using models in SAS software (SAS, Version 9.4; SAS Institute Inc., Cary, NC, USA) [30]. The experimental unit was sheep. Model applied: Yi = μ + Ti + ei where Y is the overall model, μ = grand mean, T = treatment, P = time period, e = experimental error and i = number of treatments. The experimental data are presented as the mean across the different treatments together with the standard error of the mean (SEM). Effects were determined to be significant at p < 0.05. The incomplete change over design was chosen over alternatives because (i) it reduces the risk of carry-over effects by not requiring each animal to switch back to the other treatment and (ii) the study focuses on the comparison of fewer treatments.

3. Results

The chemical composition of the alfalfa haylage (AH), corn grain (corn) and barley grain (barley) used in the study is presented in

Table 1. Chemical composition of alfalfa haylage, corn grains and barley grains (g kg⁻¹ DM, unless otherwise stated).

Chemical Parameter	AH		Corn		Barley
	Mean Value	SD	Mean Value	SD	Mean Value	SD
DM	624.6	21.1	916.8	7.8	908.1	6.6
OM	923.2	9.1	946.8	20.1	952.6	22.4
CP	166.2	3.0	88.7	0.7	100.5	6.0
Starch	23.2	5.2	688.3	7.64	536.5	14.7
NDF	496.0	22.4	215.8	46.0	205.7	39.4
ADF	370.2	32.7	28.6	1.1	90.3	8.6
Butyric acid	3.35	0.72	ND		ND
Lactic acid	23.4	3.72	ND		ND
Acetic acid	3.7	1.58	ND		ND
NH3-N (g kg−1 total N)	20.37	4.0	ND		ND
pH	5.49	0.12	ND		ND

AH, alfalfa haylage; Corn, corn grain; Barley, barley grain; SD, standard deviation; DM, dry matter; OM, organic matter; CP, crude protein; NDF, neutral detergent fibre; ADF, acid detergent fibre; ND, not determined.

.

The AH (Table 1) had an acceptable crude protein (CP) content typical of high-protein forages, along with high neutral detergent fibre (NDF) and acid detergent fibre (ADF) levels. The fermentation quality parameters of the AH in the silo were consistent with its high dry matter (DM) content. Lactic acid was the primary organic acid present, while ammonia levels remained low.

The high-energy feeds used in the study, corn and barley, both exhibited high DM and starch contents. Corn contained a higher starch content but lower CP compared to barley grain (Table 1).

Table 2. The effect of partial or complete replacement of corn by barley on the daily voluntary feed intake and digestibility of the ration based on alfalfa haylage fed to wether sheep.

Item	CG	CG67	BG67	BG	SEM	p-Value
Intake of total g d−1
Full diet DM	1438 b	1270 c	1453 ab	1583 a	51.06	<0.0001
DM haylage	913 b	755 c	926 b	1045 a	50.52	<0.0001
CP	181.7 b	164.3 c	193.5 b	222.7 a	8.29	<0.0001
NDF	341 ab	294 b	385 ab	417 a	26.81	0.0001
ADF	146.3 c	134.9 c	210.8 b	276.1 a	22.04	<0.0001
Starch	383.2 a	338.1 b	340.8 b	312.5 c	5.52	<0.0001
Intake of g kg−1 M0.75
Full diet DM	74.4 a	66.9 b	74.1 a	79.4 a	2.82	<0.0001
DM haylage	47.2 a	39.9 b	47.2 a	52.5 a	2.79	0.0004
CP	9.4 bc	8.7 c	9.9 b	11.2 a	0.48	<0.0001
NDF	17.6 bc	15.5 c	19.6 ab	20.9 a	1.36	0.0010
ADF	7.5 c	7.1 c	10.6 b	13.7 a	1.05	<0.0001
Starch	19.8 a	17.8 b	17.4 b	15.6 c	0.23	<0.0001
Digestibility (g kg−1 DM)
DM	643 b	730 a	684 ab	670 b	24.36	0.0058
CP	750 b	696 b	763 b	828 a	20.96	<0.0001
NDF	532 ab	459 b	522 b	615 a	41.94	<0.0001
ADF	457 ab	417 b	425 b	549 a	49.16	<0.0001
Starch	926 a	943 a	845 b	923 a	15.24	<0.0001

CG, corn only; CG67, corn grain 67%, barley grain 33%; BG67, barley grain 67%, corn grain 33%; BG, barley supplement; DM, dry matter; CP, crude protein; NDF, neutral detergent fibre; ADF, acid detergent fibre; SEM, standard error of the mean; numbers in the same row marked with the same letters does not differ significantly (p > 0.05).

presents the effects of partially or fully replacing corn with barley on the daily voluntary feed intake and digestibility of AH-based rations fed to wether sheep.

DM intake (DMI) (g d⁻¹ and g kg⁻¹ M^0.75) was lower (p < 0.001) in CG67 compared to the other feeding treatments, which all achieved similar DMI levels. However, DM digestibility was higher (p < 0.001) in CG67 than in the CG and BG treatments, while remaining similar in BG67. Voluntary intake and digestibility of CP were higher (p < 0.001) in BG than in the other treatments. Intake of dietary fibre (NDF and ADF) was greater in BG and BG67 than in CG and CG67. Fibre digestibility was highest in BG compared to CG67 and BG67.

Starch intake decreased as the proportion of corn in the concentrate declined, reaching its lowest level in BG (p < 0.001). Starch digestibility was lowest (p < 0.001) in BG67 compared to the other treatments, which showed no significant differences among themselves (p > 0.05).

Table 3. The effect of partial or complete replacement of corn grains by barley grains on the nitrogen balance (g d⁻¹) and water balance (ml d⁻¹) of the ration based on alfalfa haylage fed to wether sheep.

Item	CG	CG67	BG67	BG	SEM	p-Value
N intake haylage	29.07 b	26.29 c	30.95 b	35.63 a	1.32	<0.0001
N intake concentrate	13.01 c	14.69 a	14.12 b	14.73 a	0.18	<0.0001
Total N intake	42.07 c	40.97 c	45.07 b	50.36 a	1.41	<0.0001
Faecal N	7.16 a	7.75 a	7.37 a	6.14 b	0.48	0.0097
Urinary N	12.27 a	8.79 b	9.04 ab	12.44 a	1.66	0.0425
N balance	22.64 c	24.43 bc	28.66 ab	31.79 a	2.23	0.0004
Water intake by water	2748	2702	2883	3029	187.63	0.3051
Water intake by the ration	591.5 c	504.3 a	604.8 bc	666.6 b	32.98	<0.0001
Total water intake	3339 ab	3206 b	3487 ab	3695 a	199.61	0.0942
Total water intake g kg−1 M0.75	142.5	142.1	147.6	151.6	10.02	0.7470
Urinary water excreted	1017	1215	1297	1102	163.98	0.0606
Faecal water excreted	1151 a	765 b	798 b	1299 a	84.05	<0.0001
Total water excreted	2169 a	1980 b	2095 ab	2402 ab	157.0	0.0406
Water balance	1170	1226	1393	1294	179.07	0.6368

CG, corn only; CG67, corn grain 67%, barley grain 33%; BG67, barley grain 67%, corn grain 33%; BG, barley supplement; N, nitrogen; SEM, standard error of the mean; numbers in the same row marked with the same letters does not differ significantly (p > 0.05).

presents the effects of partial or complete replacement of corn with barley on the nitrogen and water balance of AH-based rations fed to wether sheep.

The BG treatment had higher nitrogen (N) intake from AH (p < 0.001), greater total N intake (p < 0.001), and lower faecal N excretion (p < 0.01) compared to the other treatments, which showed no differences in faecal N excretion. BG67 also had higher total N intake (p < 0.001) than CG and CG67. This resulted in a higher N balance in BG, comparable to BG67. The CG and CG67 treatments had similar N balances, while BG67 had a significantly higher N balance than CG (p < 0.001).

Treatments BG and BG67 had higher water intake via feed compared to CG67 (p < 0.001). Total water intake (feed plus drinking water) was lower in CG67 (p < 0.05) than in the other treatments, which did not differ significantly from each other (p > 0.05). Faecal water excretion was greater in BG and CG than in CG67 and BG67. No significant differences were observed in overall water balance among the treatments.

4. Discussion

4.1. Feed Chemical Composition

The chemical composition of alfalfa haylage (AH) reflects a haylage with high dry matter (DM) content and limited fermentation. The ensiling technique—bales wrapped in plastic film—requires a forage DM content above 40% and longer chopping. These conditions help the bales retain their shape and allow stacking without damaging the plastic film [31]. Consequently, fewer fermentation acids are produced, resulting in a higher final pH of the ensiled forage. Lactic acid was the predominant organic acid, while ammonia nitrogen concentration remained below 50 g NH₃-N kg⁻¹ total N, indicating minimal proteolysis and good overall preservation quality [32]. The average crude protein (CP) content in the AH was lower than the 204.4 g kg⁻¹ DM reported for high quality forage [33]. It was also below values of 183 g kg⁻¹ DM at full bloom and 252 g kg⁻¹ DM at early bloom maturity stages [34]. Interestingly, although CP was lower than expected, neutral detergent fibre (NDF) and acid detergent fibre (ADF) levels fell within the range reported for AH harvested between early and late bloom stages [34].

The DM content of corn grain (corn) and barley grain (barley) was consistent with previously reported values, while the starch content was slightly lower and crude protein content slightly higher than typically reported [11,35]. As expected, corn contained more starch but less CP than barley [9], a pattern confirmed in this study (Table 1). This composition supports the use of barley to better synchronise with the rapidly degradable protein in AH, potentially enhancing ruminal microbial efficiency [36].

4.2. Feed Intake and Digestibility

The level of intake is within the expected physiological range for maintenance in sheep, and the slightly higher body weight of the study animals may partially explain the elevated intake values [15]. DMI is influenced by body weight, production level, and diet quality such as of palatability and digestibility. Adult sheep typically consume around 1.5% of body weight for maintenance, and up to 2–3% when fed ad libitum [37], which is consistent with the values observed in this study and suggests sufficient dietary acceptability across feeding treatments.

At high neutral detergent fibre (NDF) levels, rumen fill can limit intake, whereas at low NDF levels, energy intake becomes the limiting factor [38]. In this study, barley had lower NDF and higher ADF compared to corn yet neither partial (67%) nor full replacement of corn with barley reduced DMI, indicating that dietary NDF did not fall below thresholds that constrain intake [39]. This also suggests that despite barley’s lower NDF, its ADF content and the overall fibre structure of the diets were sufficient to maintain optimal rumen function and intake [40].

Animals fed the CG, BG67 and BG diets had similar DMI and dry matter digestibility, supporting previous evidence that similar intake generally results in similar digestibility [41]. This is important in designing sustainable feeding programmes for sheep that maintain animal performance while optimising nutrient use and minimising environmental impact [42].

While some researchers reported lower DMI in cows fed barley versus corn due to faster rumen fermentation and pH reduction [43], no such effects were observed in this study. This may be attributed to the inclusion rates used here (30 g kg⁻¹ M^0.75), which likely prevented excessive rumen acidification. Corn’s slower fermentation supports a higher rumen pH and propionate production, potentially enhancing carcass quality [44].

However, DMI can also be affected by the amount of concentrate used. Previous studies used higher supplementation levels (1100 g d⁻¹ from 25 to 47 kg BW) observed different outcomes compared to the lower levels used in this study (500–700 g d⁻¹ for 54 kg BW) [45]. This more conservative supplementation approach aligns with sustainable, cost-effective feeding practices.

Treatment CG67 showed the lowest DMI but highest digestibility, indicating that nutrient absorption may improve as intake decreases, possibly due to a slower passage rate and more complete ruminal degradation. Such findings are consistent with literature suggesting that reduced intake can prolong rumen retention time, enhancing fibre breakdown and microbial activity [46,47]. Nonetheless, higher intake often results in greater total digestible nutrient intake, even when digestibility slightly decreases [48] highlighting the trade-off between efficiency and throughput in feed utilisation.

Barley contained less starch compared to corn, resulting in the lowest starch intake in the BG. While total-tract starch digestibility remained stable with 67% corn replacement, full replacement slightly reduced it (92.28% vs. 90.50%) [16]. This reduction is likely due to decreased rumen pH and incomplete starch degradation in the hindgut [16,49] although some studies have reported improved starch digestibility at higher barley inclusion levels due to its faster degradation rate [50].

All diets supplied sufficient CP (around 160 g CP kg⁻¹ DM) to support DMI and digestion [51]. However, nitrogen intake appeared to be influenced more by energy source than by CP concentration alone. Sheep fed the barley-only supplement consumed more nitrogen and showed higher CP digestibility. This suggests that the synchrony between rapidly degradable protein (from AH) and readily fermentable starch (from barley) may have enhanced nitrogen retention and microbial protein synthesis. Similar trends observed in cattle, where barley diets improved CP digestibility [52], further support this mechanism.

Although rapid barley fermentation can reduce fibre digestibility when pH drops [50] this study did not observe such effects—possibly due to level of grain intake and the lower digestibility of corn components [20,53]. These results highlight the importance of matching grain inclusion levels to forage type and animal requirements to avoid negative ruminal pH effects. Overall, barley’s higher rumen degradability, improved nitrogen utilisation, and potential to reduce metabolic disorders support its use as a viable component of sustainable feeding strategies.

4.3. Nitrogen Balance

Nitrogen intake was primarily influenced by AH content in the diet, given its high soluble protein fraction. However, the higher CP content of barley also contributed to a greater total N intake in the barley-only treatment (BG). Despite these intake differences, total nitrogen excretion (faecal + urinary) did not differ significantly across treatments, suggesting that N utilisation efficiency, rather than total intake, plays a more critical role in determining excretion levels. The BG treatment exhibited lower faecal N excretion, while CG67 had reduced urinary N excretion, which may reflect a more favourable energy-to-protein synchrony in these groups. Increased energy availability from barley (rapidly fermentable starch) likely promoted greater microbial protein synthesis, capturing more N in the rumen and reducing losses via faeces and urine. This supports the principle that optimal synchronisation of carbohydrate and nitrogen availability enhances microbial efficiency and lowers waste [54,55].

In contrast, corn-based treatments (CG, CG67, BG67) were associated with increased faecal N excretion, a finding consistent with studies reporting enhanced post-ruminal fermentation from slowly fermentable starch sources [20]. Postruminal starch fermentation in corn diets can shift microbial activity to the hindgut, where microbial protein is largely excreted rather than absorbed, thereby increasing faecal N output [56,57]. This may reduce the efficiency of nitrogen capture into productive pathways and increase the environmental footprint of the diet. Since urinary N is more volatile and prone to ammonia emissions, strategies that lower urinary N—such as partially replacing corn with barley—may significantly benefit environmental outcomes. Overall, the improved nitrogen utilisation observed with barley inclusion, especially in the BG treatment, highlights its potential for reducing nitrogen losses and supporting more sustainable feeding practices. These results underline the importance of selecting carbohydrate sources not only based on energy content but also on their fermentability characteristics and synchronisation with forage-derived nitrogen, especially in high-CP forage systems like those based on alfalfa haylage [55].

4.4. Water Balance

Ad libitum water intake results indicated that approximately 15–18% of total water intake was derived from the diet, aligning with previous reports [58]. Voluntary water intake is influenced by dry matter intake (DMI), diet composition, and particularly the energy and fibre content of the ration [59]. Additionally, animal behaviour, environmental conditions (e.g., ambient temperature, humidity), and physiological status (e.g., growth, metabolism) influences water intake [60].

Energy-dense, starch-rich diets such as those based on corn may increase metabolic water requirements due to greater oxidation demands and urea excretion, especially when protein synchrony is suboptimal [61]. In contrast, barley’s higher fibre content may enhance rumen fermentation and stimulate saliva production, which helps buffer rumen pH and may influence drinking behaviour indirectly [60]. Despite these compositional differences, no significant treatment effects were detected for total water intake, suggesting that sheep have a strong homeostatic regulation of hydration, modulated more by physiological demand than by variations in feed composition.

5. Conclusions

This study demonstrated that partial or full replacement (30 g kg⁻¹ M^0.75) of corn with barley in alfalfa haylage-based diets improved dry matter intake, nutrient digestibility, and nitrogen utilisation in wether sheep. While corn provided more starch, barley supplementation resulted in better synchrony with the rapidly degradable protein in alfalfa haylage, enhancing microbial protein synthesis and reducing nitrogen losses. These findings suggest that barley is a nutritionally efficient and potentially more sustainable carbohydrate source in high-protein forage systems.

However, the study was conducted under controlled conditions with a moderate supplementation level and a single sheep breed. Results may differ under commercial conditions, different genetic backgrounds, or varying forage qualities. Additionally, outcomes such as long-term animal performance, health status, or carcass traits were not assessed.

From a practical standpoint, barley presents a viable alternative to corn, especially in regions where alfalfa or other protein-rich forages are abundant. Its inclusion can enhance nitrogen efficiency and help reduce environmental nitrogen losses, without negatively affecting intake or digestibility.

Future research should investigate the long-term effects of barley-based supplementation on growth performance, meat quality, and nitrogen emissions across diverse production systems to better inform sustainable feeding strategies.