LAUSR

This study was conducted to evaluate the effects of the forage-to-concentrate ratio of the partial mixed ration (PMR) and the quantity of concentrate offered in an automated milking system (AMS), in a feed-first guided-flow barn, on the behavior and performance of dairy cows. Eight ruminally cannulated multiparous Holstein cows were used in a replicated 4 × 4 Latin square balanced for carry-over effects. Treatments were arranged in a 2 × 2 factorial consisting of a PMR that contained (dry matter basis) either a low (54:46; L-FOR) or a high (64:36; H-FOR) forage-to-concentrate ratio and AMS concentrate provision to achieve low (2 kg/d; L-AMS) or high (6 kg/d; H-AMS) intake. Each period consisted of 28 d with 6 d for dietary transition, 13 d for adaptation, and 9 d of collection. The first 4 d of data and sample collection were used to evaluate behavioral data (milking frequency, feeding behavior, and standing and lying behavior) and ruminal pH. Subsequently, a sampling device removal day was provided, and the last 4 d were used to evaluate ruminal fermentation and apparent total-tract digestibility. All 9 d were used for milk yield measurement, and the 8 d were used for dry matter intake measurement. Cows fed the H-AMS consumed 3.5 kg/d less PMR while consuming 4.2 kg/d more AMS concentrate, but total dry matter intake (PMR+AMS) was not affected by treatments averaging 27.3 kg/d. Although cows fed H-AMS had greater concentrate intake, they also had greater variability for AMS concentrate intake among days (0.85 vs. 0.25 kg/d, respectively). The number of PMR meals and PMR eating behavior were not affected by the PMR or AMS treatments. Feeding H-AMS did not affect milking frequency averaging 3.63 milkings/d, but tended to increase milk yield by 1.25 kg/d relative to L-AMS. Likewise, cows fed the L-FOR tended to have greater milk yield relative to H-FOR (39.3 vs 37.9 kg/d, respectively), but had greater holding area time. Minimum ruminal pH tended to be lower for cows fed L-FOR compared with cows fed H-FOR but was not affected by the AMS concentrate treatment. When fed the L-FOR, feeding the H-AMS increased total short-chain fatty acid concentration in the rumen relative to cows fed L-AMS, whereas the response for H-FOR was not affected by the AMS concentrate. These data suggest that feeding H-AMS may improve milk yield, but also increases the day-to-day variability in AMS concentrate consumption. Feeding a L-FOR PMR may increase milk yield without affecting variability in AMS concentrate consumption; however, it may reduce ruminal pH and increase the time spent in the holding area compared with cows fed a H-FOR PMR.