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Beginning in September 1997, a 6-week study was conducted to compare performance and income-over-feed cost of lactating Holsteins cows fed either a total mixed ration diet (TMR) only, compared to TMR in the afternoon and pasture in the morning, or TMR in the morning and pasture in the afternoon. Fifty-four Holstein cows in midlactation, averaging 28.1 kg/d of milk, were used in the study. Cows were on pasture for 8 h/d after either the p.m. or the a.m. milking. Predominantly orchardgrass with lesser amounts of white clover and Kentucky bluegrass were grazed. Pasture was sampled once per week, and weekly composites were analyzed. Compressed sward height and herbage dry matter (DM) yield were estimated once per week. Milk yield was electronically recorded and was sampled biweekly. Body condition score and body weight (BW) was recorded at the beginning and end of the study. Income-over-feed cost was calculated for each treatment. Compressed sward height and DM yield averaged 12.7 cm and 1397 kg/ha, respectively. Pasture crude protein, neutral detergent fiber, and acid detergent fiber averaged 27.0, 55.7, and 26.9%, respectively, and net energy-lactation was 1.65 Mcal/kg of dry matter. Milk production was greater for cows on the TMR treatment (29.1 vs. 28.2 and 27.6). No significant difference occurred in percentage of milk fat (3.54, 3.42, and 3.46%), or protein (3.28, 3.20, and 3.22%) for the above respective treatments. The SNF content (8.77 vs. 8.67 and 8.63%) was higher in TMR cows. While BW change did not differ among treatments (23, 32, and 22 kg), body condition score change was greater in cows fed TMR only (0.14 vs. -0.06 and 0.01). As expected, TMR intake was greatest for cows fed TMR only and lowest for cows grazing after the p.m. milking (26.6 vs. 20.3 vs. 17.5 kg/d dry matter). Income-over-feed cost differed between treatments and was approximately 18.6 and 7.5% higher for cows grazing high quality pasture during the afternoon and the morning, respectively, compared with cows on the TMR treatment.
Soriano et al. (Thu,) studied this question.