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Milk from yaks, also called "liquid gold", is reputed to be very healthy for people, but the yield is relatively low. The intake of energy and amino acids, especially lysine and methionine, of grazing, lactating yaks are often below requirements and this could explain, at least in part, the low milk yield. We hypothesized that grazing, lactating yaks, supplemented with energy and/or amino acids, would improve their performance and the average daily gain (ADG) of their calves. Twenty-four multiparous yaks (218 ± 5.3 kg), blocked by bodyweight, were offered one of four dietary treatments (n = 6 yaks per treatments) as: 1) no supplement (CON); 2) 15.0 g/d rumen-protected lysine plus 5.0 g/d rumen-protected methionine (SA); 3) 1.20 kg/d concentrate (SC); and 4) both SA and SC (SAC). The ADG was greater (P < 0.001) in yaks with than without supplementary concentrate, whereas the greatest ADG for calves was in the SAC group (interaction, P = 0.034). The concentration of ruminal total volatile fatty acids (VFAs) and of butyrate increased (P < 0.01) in yaks with supplementary concentrate, whereas iso-VFAs increased (P < 0.01) in yaks with supplementary rumen-protected lysine plus methionine (RPLM). The relative abundances of the ruminal bacteria Prevotella brevis and Ruminococcus albus increased (P < 0.01) in yaks with supplementary concentrate or RPLM, with the greatest abundance (interaction, P < 0.05) in the SAC group. Milk yield from hand-milking, and the concentrations of fat, protein, total solids and urea were not affected by dietary supplements, but lactose concentration increased (P = 0.021) with concentrate supplementation, whereas somatic cell count decreased (P < 0.01) when yaks received either supplementary concentrate or RPLM. Milk lysine and methionine, as proportions of total amino acids (TAAs), and concentration of TAAs increased with supplementary concentrate or RPLM. The milk concentrations of C16:1, C18:2n-6c and C18:3n-6 increased (P < 0.05) in yaks supplemented with concentrate, whereas, the concentrations of saturated, monounsaturated, and polyunsaturated fatty acids were not affected (P > 0.05) by treatments. These results indicated that the ADG of calves improved, whereas the rumen fermentation capacity of the lactating yaks was enhanced with supplementary concentrate and RPLM. It was concluded that dietary supplements could be an effective management option to improve performance in grazing, lactating yaks and the ADG of their calves raised on the Qinghai-Tibetan Plateau. • Supplements improved average daily gain in lactating yaks and calves. • Concentration of volatile fatty acids increased with supplementary concentrates. • Somatic cell count declined with supplementary concentrate or lysine + methionine. • Lysine and methionine in yak milk increased with supplements. [ABSTRACT FROM AUTHOR]

Yaks (Bos grunniens) and Qaidam cattle (Bos taurus) graze the Qinghai-Tibetan Plateau (QTP) grassland all year, but yaks graze at altitudes higher than cattle. Yaks are raised by vertical transhumance, grazing at higher altitudes in summer and lower altitudes in winter. It is mainly in winter, when forage is of poor quality, that the two species co-graze. At this time, yaks do not receive supplements or shelter while cattle require supplements and night shelter. Previous studies reported that both energy and protein utilization were greater in yaks than cattle, and the rumen microbiota differed between the species. Based on the differences between species, we hypothesized that the rumen microbiota would enable yaks to digest a poor quality diet to a greater extent than cattle. This could explain why yaks are able to overcome the harsh winter without supplements while grazing poor quality pasture, but cattle require supplements. To test the hypothesis, fermentation parameters were studied in vitro using rumen inocula from yaks and cattle. Four isonitrogenous substrates of different energy levels (6.62, 8.02, 9.42, 10.80 MJ ME/kg) were used. The neutral and acid fiber detergent digestibilities were greater (P < 0.05) in yaks than in cattle and both increased linearly (P < 0.05) with increasing energy level. Methane production was lesser (P < 0.05) in yaks than cattle, and decreased linearly (P < 0.05) with increasing energy level. Concentrations of total volatile fatty acids (VFAs) and acetate, the ratio of acetate to propionate, and ammonia-N (except at 48 h) were greater (P < 0.05) in yaks than cattle; whereas concentrations of propionate (except at 6 h), butyrate, and iso-VFAs were lesser (P < 0.05) in yaks than cattle. In addition, total VFAs, propionate, butyrate, and ammonia-N increased linearly (P < 0.05), whereas, acetate and the ratio of acetate to propionate decreased linearly (P < 0.05) with increasing energy level. The relative abundance of Bacteroidetes was greater (P < 0.05), whereas of Firmicutes and the ratio of Firmicutes to Bacteroidetes were lesser (P < 0.01) in yaks than cattle, and Bacteroidetes decreased linearly (P < 0.001), whereas Firmicutes and the ratio of Firmicutes to Bacteroidetes increased linearly (P < 0.01) with increasing energy levels. The relative abundances of fibrolytic bacteria (e.g. Rikenellaceae_RC9_gut_group and Butyrivibrio) and of H 2 -incorporating bacteria (e.g. Quinella) were greater (P < 0.05), whereas, amylolytic bacteria (e.g. Selenomonas and Succiniclasticum) and of H 2 -producing bacteria (e.g. Lachnospiraceae_NK3A20_group and Ruminococcus) were lesser (P < 0.05) in the rumen inoculum from yaks than cattle. It was concluded that the greater relative abundance of fibrolytic and H 2 -incorporation bacteria and lesser H 2 -producing bacteria enable yaks to better digest fibers and produce less CH 4 than cattle. • Methane production and H 2 -producing bacteria were lesser in yaks than cattle. • Fiber digestion and fibrolytic bacteria were greater in yaks than cattle. • Total volatile fatty acid and ammonia-N were greater in yaks than cattle. • Bacteroidetes decreased, whereas Firmicutes increased with increasing energy levels. [ABSTRACT FROM AUTHOR]

• Rumen protected lysine and methionine improved average daily gain in Tan lambs. • Digestibility of nutrients decreased linearly with an increase in feed level. • Rumen protected lysine and methionine improved nitrogen-retention. • Rumen protected lysine and methionine improved microbial protein synthesis. Effect of feed level (FL) and supplementary rumen protected lysine (Lys) and methionine (Met) (RPLM) on growth performance, rumen fermentation, blood metabolites, and nitrogen (N) balance was studied in growing lambs fed low protein diets. Thirty-six, 7-month old wether Tan lambs (initial body weight, 35.0 ± 1.66 kg) were assigned into one of six groups (n = 6) in a randomized complete block design. The experiment was a 2 × 3 factorial arrangement of treatments. The lambs were either not supplemented (control) or supplemented (RPLM) with 4.5 g/day rumen protected Lys plus 1.5 g/day rumen protected Met and combined with three FLs (1.0, 0.8 and 0.6 voluntary intake - VI). The basal diet, on a dry matter (DM) basis, consisted of 400 g/kg forage and 600 g/kg concentrate. The average daily gain (ADG) increased linearly (P < 0.05) with increasing FL, and ADG was greater (interaction, P = 0.01) and the DM intake to ADG ratio was lesser (interaction, P = 0.04) in RPLM than control lambs in the 0.8 VI and 1.0 VI FLs, but not in the 0.6 VI FL. Digestibilities of DM, organic matter, crude protein, neutral detergent fiber and acid detergent fiber decreased linearly (P < 0.01) with increasing FL. Concentrations of total volatile fatty acids (VFAs) and butyrate and the acetate:propionate ratio increased linearly with increasing FL (P < 0.05). In addition, concentrations of propionate and iso-VFAs were greater (P < 0.05); whereas, of butyrate and the acetate: propionate ratio were lesser (P < 0.05) in RPLM than control lambs. Daily faecal-N output and N-retention were greater (interaction, P < 0.05) in RPLM than control lambs in the 1.0 VI and 0.8 VI FLs, but not in the 0.6 VI FL. In addition, microbial-N (MN) and the efficiency of microbial protein synthesis increased linearly (P < 0.01) with increasing FL and MN was greater (P = 0.02) in RPLM than in control lambs. Serum glucose concentration increased linearly (P < 0.01) with decreasing FL and was greater (P < 0.01) in RPLM than in control lambs. It was concluded that supplementary RPLM at 1.0 VI and 0.8 VI could improve ADG, feed conversion, and N-balance in growing Tan lambs and could be beneficial for sheep fed a low protein diet. [ABSTRACT FROM AUTHOR]

• Fermentation of Tibetan (TBI) and Small-tailed Han sheep rumen inocula (HSI) differed. • CH 4 and H 2 decreased with an increase in proportion of TBI. • Nutrient digestibilities increased with an increase in proportion of TBI. • Ratios of TBI: HSI inocula affected estimated Gibbs energy changes. • Metabolic hydrogen fluxes were shifted by ratios of TBI: HSI inocula. Tibetan sheep are well adapted to harsh environmental conditions and poor-quality forage and are known to produce less methane (CH 4) gas than lowland sheep. In this study, rumen inocula from Tibetan sheep (TBI) and from Small-tailed Han sheep (HSI) were incubated in in vitro batch cultures in five ratios (TBI: HSI): 0:100, 25:75, 50:50, 75:25 or 100:0 for 72 h. With an increasing proportion of TBI, there was a linear decrease (P < 0.001) in gas and CH 4 production on a degraded dry matter (DM) basis at 12, 24, 48 and 72 h. In addition, increasing the proportion of TBI increased the digestibility of DM (P < 0.05), neutral detergent fiber and acid detergent fiber and total and individual volatile fatty acids (VFA) concentrations at almost all time points. An increase in the TBI: HSI ratio resulted in less metabolic hydrogen ([2H]) incorporated into CH 4 and more into propionate. The recovery of [2H] consistently decreased with an increase in the TBI: HSI ratio, indicating the existence of unaccounted [2H] in TBI. It would be important to study the rumen microbiome in Tibetan sheep with the use of classical microbiology and modern –omics techniques to identify [2H] sinks alternative to CH 4 , which could perhaps be stimulated in other domestic ruminants. [ABSTRACT FROM AUTHOR]