Productive Response of Dairy Cows Fed with Different Levels of Totally Mixed Ration and Pasture

SALADO, ELOY EDUARDO; BRETSCHNEIDER, GUSTAVO; CUATRIN, ALEJANDRA; DESCALZO, ADRIANA MARÍA; GAGLIOSTRO, GERARDO ANTONIO

Agricultural Sciences

Scientific Research Publishing (SCIRP)

Año: 2018 vol. 09 p. 824 - 851

2156-8553

Forty multiparous Holstein cows in early lactation (66 ± 19 days) were assignedto one of four treatments that consisted in different ratios of totalmixed rations (TMR) and pasture at 100% TMR (T0), 75:25 (T1) 50:50 (T2)and 25:75 (T3) over 9 weeks in autumn-winter. Measures of rumen parametersand digestion were performed on 4 additional Holstein cows in late lactation(287 days postpartum) fitted with permanent ruminal fistulae and producing22.6 (±5.4) kg milk in a 4 × 4 Latin Square design. In T1 to T3 cowswere taken to the grazing plot once they finished the pre-planned TMR intakeand pasture was offered at 2 times the expected forage DM intake. Milk wasanalyzed for chemical composition, milk fatty acid (FA) profile and antioxidantcompounds. The cows were individually weighed and body conditionscore (BCS) was determined. After the morning milking, blood samples weretaken every 2 weeks and plasma was analyzed for glucose, urea, non-esterifiedfatty acids (NEFA), insulin, growth hormone (GH) and insulin-like growthfactor (IGF-I). Herbage mass in pre grazing strips of pasture averaged 2540 ±343 kg DM/ha. As TMR intake increased, production variables increased linearlyexcepting milk fat (3.88 g/100g) and milk protein (3.43 g/100g) contentsthat were not affected. Milk yield (kg/cow/d) resulted maximal in T0(34.2) and linearly decreased (p < 0.01) with pasture intake averaging 32.1(T1), 28.4 (T2) and 26.8 (T3) as a higher energy intake and a lower energycost associated with grazing activity. Milk fat output (kg/cow/d) resultedhigher in T0 (1.35) and T1 (1.25) compared to T2 (1.10) and T3 (1.04). Milkprotein yield (kg/cow/d) was also higher in T0 (1.18) and T1 (1.11) comparedto T2 (0.96) and T3 (0.92). Total DM (24.09 kg/cow/d) and energy (41.95 Mcal NEL/cow/d)) intakes resulted maximal in T0 decreasing as pasture replacedTMR without effects on conversion efficiency (1.48 kg milk/kg DM).Plasma concentration of glucose, insulin and IGF-I were not affected but GHand NEFA increased as pasture replaced TMR in T3. Ruminal pH (5.91) andtotal or VFA proportions did not differ but NH3-N concentration resultedhigher in treatments with higher proportion of pasture. Kinetic parameters ofDM and NDF digestion from pasture or corn silage were not affected. MilkFA profile and milk antioxidant quality showed unfavorably changes as TMRincreased by a decrease in rumenic and linolenic acids and content of antioxidant vitamins, without effect on the atherogenicity index. Results suggested a depressing effect of the pasture on total DM and energy intake probably explained by qualitative deficiencies chemical composition of the forage and/or factors that affect animal behavior that may induce losses in body condition of high yielding dairy cows.