Effects of the Amount of Concentrate Offered in an Automated Milking System on dry matter intake, Milk Yield, Milk Composition, Ruminal fermentation, and Behaviour of Primiparous Holstein Cows Fed Iso-Caloric Diets

The objective of this study was to determine if the quantity of concentrate provided in an automated milking system (AMS) affects dry matter intake (DMI), attendance to the AMS, milk and milk component yield, feeding behaviour, cow activity and ruminal fermentation of lactating dairy cows fed iso-caloric diets. Eight ruminally-cannulated primiparous Holstein cows were used in a replicated 4 × 4 Latin square design with 28-d periods. Cows were housed in a free-stall facility with a guided-traffic (feed-first) flow barn-design. Cows were offered 0.5, 2.0, 3.5, or 5.0 kg/d DM of pellet in the AMS, with an equivalent reduction of the same pellet in the partial mixed ration (PMR). Day 21 to 24 of each treatment period were used for DMI, milking performance, behaviour, and ruminal pH determination, while d 25 to 28 were used for ruminal short-chain fatty acid (SCFA) and ammonia concentrations, as well as total tract digestibility. As imposed, consumption of AMS pellet linearly increased (P < 0.01), equating to 0.50, 2.00, 3.49, and 4.93 kg/d. Correspondingly, the standard deviation in AMS pellet intake among days linearly increased from 0.06 to 0.85 kg/d as the quantity of concentrate in the AMS increased from 0.5 to 5.0 kg (P < 0.01). The PMR DMI decreased linearly with increasing AMS concentrate allocation (P < 0.01), but total DMI (PMR + AMS concentrate) was not affected (25.3 kg/d, P = 0.40). As AMS concentrate allocation increased, the selection against particles retained on an 18-mm sieve linearly increased (P = 0.02) and selection against particles retained on the bottom pan decreased (P < 0.01). Milking frequency (3.22 milkings/d, P = 0.82), milk yield (37.5 kg/d, P = 0.59), milk fat yield (1.43 kg/d, P = 0.46), and milk protein yield (1.22 kg/d, P = 0.42) were not affected; however, milk urea nitrogen concentration decreased linearly with increasing AMS concentrate (P = 0.02). Ruminal pH averaged 6.18 and was not affected by AMS concentrate (P = 0.62). Total ruminal SCFA concentration was greatest when 3.5 kg of concentrate was allocated in the AMS and ruminal ammonia decreased linearly with increasing AMS concentrate (P = 0.01). Time spent lying, the number of lying bouts, and average bout duration were not affected by treatment (P ≥ 0.11). These data indicate that increasing the quantity of concentrate in the AMS increases daily variability in AMS concentrate intake while decreasing PMR intake, and increasing AMS pellet provision, under isocaloric dietary settings, is not likely to affect voluntary visits to the AMS, milk and milk component yield, or ruminal fermentation.

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