ChileanJAR

Thirty Friesian autumn-calving dairy cows in their second or later lactation were used in a randomized block design, to evaluate the effect of three levels of concentrate supplementation: 1 kg (Low, L); 3.5 kg (Medium, M) and 6 kg of barley/cow/day (High, H). Animals had ad libitum access to permanent pasture silage, free access to water and minerals and 1 kg/day of grass hay. Cows were housed in individual stalls from the 3^rd to the 18^th week being the last 12 weeks, the experimental periodo The diets were isoproteic (16% CP) by using rapeseed mear in rates 0.5 and 1 kg with animals M and H, respectively. The silage had a mean dry matter content, crude protejn, in vitro digestibility, pH, N-NH₃ and metabolizable energy of 16.1 %, 15.9%,63.3%,4.5, 10.6 and 2.25 Mcal/kg of D.M., respectively. The hay dry matter content crude protein, in vitro digestibility were 80.5, 8.8, 57.8%. For silage and haythe metabolizable energywas 2.25 and 1.67 Mcal/kg of D.M., respectively. Mean daily silage jntake was 7.9; 7.6 and 7.5 kg of D.M./cow (P > 0.05) for L, M and H, respectively and total daily intake of 9.7a; 11.6b and 14.7c kg D.M. /cow (P < 0.05) for treatment L, M and H, respectively. Milk production, milk fat, and fat-corrected milk were 19.1a, 19.5a, 17.3b (P< 0.01), 3.86a, 3.72a, 3.57a (P > 0.01), 15.2b, 17.9a, 17.9a (P<0.01) for L, M and H, respectively. The response to supplementation was 1.19 kg of fat-corrected milklkg concentrate between L and M, and it was only 0.01 kg of fat-corrected milklkg concentrate between M and H. Average live weight of cows was 527a, 501c, 516b (P< 0.01) for L, M and H. respectively. It is concluded that for medium-Ievel productive cows (5,000 kg of milk/lactation) therewas a adequate response to concentrate supplementation up to 4 kg/cow/day. Over this level, only an increment of li