Effects of supplementary concentrate and/or rumen-protected lysine plus methionine on productive performance, milk composition, rumen fermentation, and bacterial population in Grazing, Lactating Yaks

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.