Triglyceride and fatty acid composition of ruminants milk, human milk, and infant formulae

A 2 years whole lactation study was carried out in EEMAC, Paysandú-Uruguay, to evaluatethe effect of two feeding strategies (grazing plus TMR and full TMR) and two levels ofexposure to environmental conditions (access or not to a compost barn duringsupplementation). An incomplete factorial design was carried on involving threetreatments: confined cows fed TMR ad-libitum in a compost barn (CB-TMR); onesessiongrazing cows supplemented with TMR in a compost barn (CB-GRAZING); and onesessiongrazing cows supplemented with TMR in an open lot (OL-GRAZING).It were evaluated two calving seasons (Autumn and Spring;16 Holstein cows/treatment/calving season) each year. Cows were milked twice aday and the milk production was recorded automatically. Milk fat and proteinconcentration were analyzed once a week from 0 to 90 DIM, once every two weeks from91 to 180 DIM, and once a month after 181 DIM. The TMR intake were determined by pen(4 cows/pen) once a week as the difference between offered and refused feed in eachpen. Herbage DMI was determined as the amount of pasture necessary to supply thedifference between net energy requirements and that provided by the TMRdiets. Individual 305-days milk yield was obtained by fitting the exponentialfunction of Wilmink (1987). Response variables were analyzed with PROC GLIMMIX of SASand mean values were declared different when Tukey test <0.05. The milk production percow was greater (P<.0001) on CB-TMR cows (10782±251L) than on CBGRAZING(8467±217L) and OL-GRAZING (8265±212L) cows. The milk production tended tobe higher in Autumn than Spring calving cows (9514±215L vs 9069±207L; P=0.070). Theproductivity for OL-GRAZING cows was around 1000L per cow lower in Spring (8077±275)than in Autumn (9173±279) calving season. The efficiency of conversion of feed intomilk was higher on confined than in grazing cows (1.54±0.026L vs 1.40±0.025L of milk perkg of DMI; P=0.0005). The DMI necessary to produce milk solids (fat+protein) was lower onconfined (9.42±0.183; kg/kg) than grazing cows (10.30±0.144; kg/kg; P=0.0008). However,the concentrate required per litre of milk was greater inconfined than in grazing cows (395g vs 278g/L; P<.0001). The confined cows had a greatermilk production per lactation and were more efficient to convert feed intomilk, despite they required a bigger input of concentrate per kg of milk produced. The milkproduction was affected by calving season when the exposition to weatherconditions during supplementation was higher.