The effect of concentrate feeding strategy and dairy cow genotype on milk production, pasture intake, body condition score and metabolic status under restricted grazing conditions

The objective of this study was to compare the effects of contrasting concentrate feeding strategies and dairy cow genotypes on milk production, pasture intake, energy balance, and metabolic status under restricted grazing conditions. Fifty-eight Holstein Friesian cows were assigned to concentrate feeding strategy and genotype treatments in a 2 ? 2 factorial arrangement, in a randomized complete block design. Treatments were balanced for days in milk, parity, previous 305-day milk yield, and body condition score (BCS). The dietary treatments offered over the 11-week experimental period were a low flat rate concentrate allowance of 1.76 kg DM/d typical of a low input system (CON, n = 29) or a "feed to yield " concentrate allowance (FY, n = 29). The FY treatment included feeding a base of 1.76 kg DM plus 0.44 kg DM of concentrates/kg of milk above the base milk yield. All cows were allocated 13 kg DM of grass. The genotype treatments consisted of lower fertility higher milk (LFHM) and higher fertility lower milk (HFLM) cows based on Economic Breeding Index figures. The FY strategy resulted in a higher milk (+ 1.77 kg/d) and a higher fat plus protein yield (+ 0.12 kg/d) and increased BCS (+ 0.12 units) compared to CON. The metabolic status of FY cows differed from CON cows as evidenced by the reduced beta-hydroxybutyrate and non-esterified fatty acid concentrations. Genotype did not influence milk output but did affect total dry matter intake (DMI) and BCS. Cows of LFHM tended to have higher yields on the FY resulting in increased milk yield of 11% compared to FY-HFLM cows. Cows of HFLM fed CON had greater fat and protein output of 0.5 kg and 0.5 kg, respectively compared to the CON-LFHM. No differences in feed efficiency was observed between treatments. Despite cows originating from a higher output herd, differences in genotype had a significant effect on the response to the concentrate feeding strategies. These observations are important when identifying suitable genotypes or feeding strategies that most suit grazing systems.