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Effect of concentrate source (cottonseed vs. barley) on milk performance and fatty acids profile of spring calving Holstein-Friesian cows feeding an indoors silage regime
Milk performance and fatty acids (FA) profile of spring-calving Holstein-Friesian cows (n=36) at end of lactation (200 days in milk) were examined. Cows were fed indoors with a total mixed ration (TMR) containing: 70% silage (grass: maize, 36:64) and 30% concentrate. Two sources of concentrate were investigated: cottonseed (C) at two levels, low (5 kg DM/cow/day) or high (7 kg DM/cow/day), and barley (B) at high level (7 kg DM/cow/day). Animals were randomly assigned to one of three indoors (n=12) feeding regimes (C5, C7 and B7), during 10 weeks in autumn. The B and C concentrates were composed of corn flour (B, 43.1 vs. C, 31.0%), soybean hulls (B, 28.5 vs. C, 34.0%), soybean meal (B, 23.5 vs. C, 20.0%), barley flour (B, 1.4 vs. C, 0%), cottonseed (B, 0 vs. C, 12.0%) amender (B, 1.0 vs. C, 1.0%), calcium carbonate (B, 1.5 vs. C, 1.0%) and dicalcium phosphate (B, 1.0 vs. C, 1.0%). Average chemical composition of B and C concentrates was: crude protein (166 vs. 168 g/kg DM), neutral detergent fibre (249 vs. 418 g/kg DM) and crude fat (31 vs. 49 g/kg DM), respectively. Daily milk yield was higher (P < 0.001) at the high level of supplementation (B7, 18.1 and C7, 17.9 kg/cow/day) compared to the low level (C5, 15.7 kg/cow/day), and dairy cows at the high level of concentrate showed higher (P < 0.05) body weight values (B7, 605 and C7, 598 kg) compared to those at the low level (567 kg). Milk protein was lower (P < 0.05) at the high level of concentrate in the cottonseed (C7, 30.7 g/kg DM) than in the barley treatment (B7, 32.7 g/kg DM). There were no differences among treatments in milk fat and milk urea content. No differences were also found among treatments in short, medium and long chain FA. Despite this, higher (P < 0.05) content of polyunsaturated FA and linoleic acid were observed in the C7 compared to the C5 treatment (2.48 and 2.22 vs. 2.16 and 1.92 g/100 g of FA). These results might be explained by alterations in rumen biohydrogenation pathways of milk FA from dairy cows supplemented with cottonseed concentrate at high level. Linolenic acid was, however, higher (P < 0.01) in the B7 (0.27 g/100 g of FA) than in the C5 treatment (0.24 g/100 g of FA).
Keywords: dairy cow, lipid feed supplements, milk fatty acids composition.