Abstract
Forty multiparous Holstein cows in early lactation (66 ± 19 days) were assigned to one of four treatments that consisted in different ratios of total mixed 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 parameters and digestion were performed on 4 additional Holstein cows in late lactation (287 days postpartum) fitted with permanent ruminal fistulae and producing 22.6 (±5.4) kg milk in a 4 × 4 Latin Square design. In T1 to T3 cows were taken to the grazing plot once they finished the pre-planned TMR intake and pasture was offered at 2 times the expected forage DM intake. Milk was analyzed for chemical composition, milk fatty acid (FA) profile and antioxidant compounds. The cows were individually weighed and body condition score (BCS) was determined. After the morning milking, blood samples were taken every 2 weeks and plasma was analyzed for glucose, urea, non-esterified fatty acids (NEFA), insulin, growth hormone (GH) and insulin-like growth factor (IGF-I). Herbage mass in pre grazing strips of pasture averaged 2540 ± 343 kg DM/ha. As TMR intake increased, production variables increased linearly excepting milk fat (3.88 g/100g) and milk protein (3.43 g/100g) contents that were not affected. Milk yield (kg/cow/d) resulted maximal in T0 (34.2) and linearly decreased (p 3-N concentration resulted higher in treatments with higher proportion of pasture. Kinetic parameters of DM and NDF digestion from pasture or corn silage were not affected. Milk FA profile and milk antioxidant quality showed unfavorably changes as TMR increased 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.
Highlights
Milk production systems in Argentina are moving towards more intensified farms to release land for the cultivation of soy (Glycine max) which is considered a more profitable activity than milk production [1]
As total mixed rations (TMR) intake increased body weight (BW) and body condition score (BCS) resulted higher (Table 4) according to the greater estimated net energy for lactation (NEL) intake (Table 3) and with the reduction of the circulating levels of NEFA, these results suggest that the animals did not use all the additional energy to increase milk production but that a part was derived to the reconstitution of body reserves
Milk yield increased linearly with increasing TMR intake in the 30% - 100% range explored for cows producing between 27 - 34 kg milk/day and was probably explained by a higher energy intake combined with a decrease in energy expenditure associated with grazing activity
Summary
Milk production systems in Argentina are moving towards more intensified farms to release land for the cultivation of soy (Glycine max) which is considered a more profitable activity than milk production [1]. In the TMR systems feeding costs are higher than in pasture representing more than 50% of the total costs [3] Besides their lower production costs, pasture-based systems are characterized by a low environmental impact [4] compared to confined systems but present nutritional limitations that hinder the expression of the production potential of high yielding dairy cows [5]. A feeding alternative is the combination of TMR and grazing which is known as a partially mixed ration (PMR) since pasture is directly grazed by the cows and not physically included in the TMR It combines partial advantages of each system and pasture would reduce the amount of TMR included in the total diet and feeding cost but may improve the dairy herd health [6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
