María Laura Villar

Nutritional management during the first year of life is critical for optimizing growth and fibre production in Angora goats managed under rangeland systems. The present study evaluated the effects of winter dietary crude protein (CP) level on productive and reproductive traits in young Angora goats. Thirty-three goats (7 months of age; 15 females, 17.9 ± 0.9 kg; 18 males, 22.1 ± 1.4 kg) were assigned to a 2 × 2 factorial arrangement (diet × sex) and housed in pens during winter for 84 d, receiving either a 15% CP (15CP) or 18% CP (18CP) diet. Goats fed 18CP exhibited greater (P < 0.05) body weight gain (BWG) and tended (P ≤ 0.10) to have higher body condition score (BCS) than those fed 15CP, whereas final BW and morphometric traits were not affected (P > 0.05). A diet × sex interaction (P < 0.05) was observed for greasy and clean fleece weight, with males fed 18CP producing more fibre than the other groups. No dietary effects were detected on reproductive traits at 18 months of age (P > 0.05). Overall pregnancy rate was 67% across treatments. Increasing dietary CP from 15% to 18% during winter improved BWG and mohair production in young Angora goats, although reproductive traits at first mating were unaffected. The results provide practical information for winter nutritional management of replacement Angora goats under cold-climate grazing conditions.

While livestock production is a significant source of greenhouse gas emissions, it remains vital for fulfilling the growing global demand for animal protein. Including by-products in ruminant diets can enhance food circularity and reduce competition for human food, while also increasing the likelihood of reducing methane (CH₄) emissions. This study aimed to evaluate the impact of fully replacing corn grain and urea in the control diet with local by-products, specifically corn distillers’ grains combined with either barley brewed grains or with wheat middlings, on enteric CH₄ emissions and performance of sheep. Diets were balanced to be isoproteic and isoenergetic with 2.6 Mcal ME/kg of dry matter (DM) and 160 g crude protein/kg DM, respectively. Corn silage is the only source of forage in the diet, and the forage-to-concentrate ratio was maintained to 60:40 on a DM basis. Twelve Highlander female sheep of 35.9 ± 3.12 kg initial body weight (BW, mean ± standard deviation), were used in a Completely Randomized Block design, with four sheep per treatment and two measurement periods under the same treatment. Experiment lasted 60 d, 30 d acclimatization and 30 d measurements. Dry matter intake (DMI) was restricted to 2.5% of BW. Enteric CH₄ emissions of individual sheep were quantified in respiration chambers over a 48 h period. Dietary treatments did not have a significant effect either on DMI or BW gain. The diet containing barley brewed grains significantly reduced total daily CH₄ production by 22.3%, CH₄ emissions per kg of DMI by 34% and energy loss as CH₄ by 38% compared to the control diet. In conclusion, the agro-industrial by-products combinations evaluated in this study effectively replaced corn grain and urea without compromising feed intake or animal performance. Additionally, the diet containing barley brewed grains significantly reduced CH₄ yield, and energy loss compared to the control diet.

Nitrate ( ) supplementation is an effective methane (CH₄) mitigation strategy for ruminants but may produce nitrite ( ) toxicity. It has been reported that rumen protozoa have greater ability for and reduction than bacteria. It was hypothesised that the absence of ruminal protozoa in sheep may lead to higher accumulation in the rumen and a higher blood methaemoglobin (MetHb) concentration. An in vivo experiment was conducted with defaunated (DEF) and faunated (FAU) sheep supplemented with 1.8% in DM. The effects of rumen protozoa on concentrations of plasma and ruminal and , blood MetHb, ruminal volatile fatty acid (VFA) and ruminal ammonia (NH₃) were investigated. Subsequently, two in vitro experiments were conducted to determine the contribution of protozoa to and reduction rates in DEF and FAU whole rumen digesta (WRD) and its liquid (LIQ) and solid (SOL) fractions, incubated alone (CON), with the addition of or with the addition of . The results from the in vivo experiment showed no differences in total VFA concentrations, although ruminal NH₃ was greater (p < .01) in FAU sheep. Ruminal , and plasma concentrations tended to increase (p < .10) 1.5 hr after feeding in FAU relative to DEF sheep. In vitro results showed that reduction to NH₃ was stimulated (p < .01) by incoming in both DEF and FAU relative to CON digesta. However, adding increased (p < .05) the rate of accumulation in the SOL fraction of DEF relative to both fractions of FAU digesta. Results observed in vivo and in vitro suggest that and are more rapidly metabolised in the presence of rumen protozoa. Defaunated sheep may have an increased risk of poisoning due to accumulation in the rumen.

It was hypothesised that the inclusion of nitrate (NO3–) or cysteamine hydrochloride (CSH) in a protein deficient diet (4.8% crude protein; CP) would improve the productivity of sheep while reducing enteric methane (CH4) emissions. A complete randomised designed experiment was conducted with yearling Merino sheep (n = 24) consuming a protein-deficient wheaten chaff control diet (CON) alone or supplemented with 1.8% nitrate (NO3–; DM basis), 0.098% urea (Ur, DM basis) or 80 mg cysteamine hydrochloride/kg liveweight (CSH). Feed intake, CH4 emissions, volatile fatty acids (VFA), digesta kinetics and NO3–, nitrite (NO2–) and urea concentrations in plasma, saliva and urine samples were measured. There was no dietary effect on animal performance or digesta kinetics (P > 0.05), but adding NO3– to the CON diet reduced methane yield (MY) by 26% (P = 0.01). Nitrate supplementation increased blood MetHb, plasma NO3– and NO2– concentrations (P < 0.05), but there was no indication of NO2– toxicity. Overall, salivary NO3– concentration was greater than plasma NO3– (P < 0.05), indicating that NO3– was concentrated into saliva. Our results confirm the role of NO3– as an effective additive to reduce CH4 emissions, even in a highly protein-deficient diet and as a source of additional nitrogen (N) for microbial protein synthesis via N-recycling into saliva and the gut. The role of CSH as an additive in low quality diets for improving animal performance and reducing CH4 emissions is still unclear.

Nitrate (NO₃^¯) is an effective non‐protein nitrogen source for gut microbes and reduces enteric methane (CH₄) production in ruminants. Nitrate is reduced to ammonia by rumen bacteria with nitrite (NO₂^¯) produced as an intermediate. The absorption of NO₂^¯ can cause methaemoglobinaemia in ruminants. Metabolism of NO₃^¯ and NO₂^¯ in blood and animal tissues forms nitric oxide (NO) which has profound physiological effects in ruminants and has been shown to increase glucose uptake and insulin secretion in rodents and humans. We hypothesized that absorption of small quantities of NO₂^¯ resulting from a low‐risk dose of dietary NO₃^¯ will increase insulin sensitivity (S_I) and glucose uptake in sheep. We evaluated the effect of feeding sheep with a diet supplemented with 18 g NO₃^¯/kg DM or urea (Ur) isonitrogenously to NO₃^¯, on insulin and glucose dynamics. A glucose tolerance test using an intravenous bolus of 1 ml/kg LW of 24% (w/v) glucose was conducted in twenty sheep, with 10 sheep receiving 1.8% supplementary NO₃^¯ and 10 receiving supplementary urea isonitrogenously to NO₃^¯. The MINMOD model used plasma glucose and insulin concentrations to estimate basal plasma insulin (I_b) and basal glucose concentration (G_b), insulin sensitivity (S_I), glucose effectiveness (S_G), acute insulin response (AIRg) and disposition index (DI). Nitrate supplementation had no effect on I_b (p > .05). The decrease in blood glucose occurred at the same rate in both dietary treatments (S_G; p = .60), and there was no effect of NO₃^¯ on either G_b, S_I, AIRg or DI. This experiment found that the insulin dynamics assessed using the MINMOD model were not affected by NO₃^¯ administered to fasted sheep at a low dose of 1.8% NO₃^¯ in the diet.