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Performance of Dairy Cows in Midlactation Fed High Quality Grass Pasture and Concentrate at Three Percents of Energy Requirements

Department of Dairy and Animal Science, The Pennsylvania State University, University Park 16802

ABSTRACT

Thirty multiparous cows rotationally grazed high quality grass pastures (predominantly Dactylis glomerata and Poa pratensis) for 140 days. Stage of lactation was 54 to 192 days at beginning of trial. Cows were offered concentrates to supply 33, 66, or 100% of requirements for net energy for lactation above maintenance; daily intakes by the three groups averaged 3.5, 7.7, and 11.5 kg. Refusal of concentrate tended to increase with supplementation. Average milk production was 19.2, 20.4, and 21.5 kg. When individual yields were compared with an initial 2-wk period prior to trial, there was no difference in decline in milk flow, except for one 28-day period in midsummer when decline by the 33% group was greater than that by the 100% group. Milk fat yields were similar. Milk protein yields by the 100% group were significantly higher than those by the 33% group. Body weight changes were similar among groups. Quality of forage was high, and yields were adequate. Changes in milk flow attributable to movement of cows to fresh pastures were +1.35 kg per cow daily. Variations in in vitro dry matter disappearance, crude protein, and dry matter of forage were positively associated with changes in milk flow.

² Institute National de Investigaciones Agricolas, Torreon, Coah., Mexico.

³ Department of Agronomy.