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Milk yield and feeding behaviour responses to two flat-rate levels of concentrate supplementation fed over a period of eight months to cohorts of grazing dairy cows, differing in genotype, body weight, or milk yield

Pieter Raedts , James Hills

Abstract

Context: In most pasture-based herds in Australia, supplementation with concentrates is normally a flat rate, with quantities determined by average cow requirements, rather than individual cow requirements. Comparisons between flat rate and individual feeding rarely show advantages such as milk yield benefits for either. However, in pasture-based systems little is understood regarding milk production responses or levels of pasture substitution, when different groups of cows within the herd are fed higher levels of concentrates. Aims: To investigate the effect on milk yield, feeding time, and ruminating time, of two flat rate levels of concentrate supplementation, fed over 8 months to 180 cows selected for one of three different parameters. Methods: Cohorts of cows were selected on contrasting differences for either milk production at the start of lactation, body weight, or genotype. Each cohort was divided into two balanced groups receiving either two or six kg DM/cow/d concentrate, from approx. 12 days in milk onwards. All cows remained part of the main milking herd (total herd size 320 spring-calving cows), with similar opportunity for all cows to graze pasture or feed on supplemented grass silage during periods of pasture shortage. Milk yield was recorded at each milking and feeding behaviour continuously recorded by MooMonitor+ collars. Results were analysed for three seasonal periods of 10, 12 and 10 weeks (P1, P2 and P3 respectively) commencing in spring. Results: Mean marginal milk response (L milk per 1 kg DM of concentrate extra) over the trial period was 0.88 L, increasing from 0.71 L in P1, to 0.92 L in P2 and 1.03 L in P3. The high concentrate cohorts recorded reduced feeding time per day of 37 minutes overall (46, 35 and 29 min for P1, P2 and P3, respectively). Significant differences were found for milk yield and feeding time between several contrasting cohorts. The lowest marginal milk response was for cross-breed cows in P1 with 0.18 L and feeding reduced by 65 min/cow/d, with the contrasting cohort of Friesian cows at a larger marginal response of 0.94 L and smaller feeding time reduction of 32 min/cow/d. Conclusions: The difference between cohorts demonstrates potential for targeted concentrate feeding to specific groups of cows that respond differently in marginal milk yield and grazing behaviour. Implications: When a significant change is made in strategic levels of concentrate feeding, the impact not only on marginal milk response should be considered, but also on pasture intake.

AN23142  Accepted 07 April 2024

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