Feeding a higher forage diet prepartum decreases incidences of subclinical ketosis in transition dairy cows.

A common feeding practice during the dry period is to switch dairy cows to an energy-dense diet 3 wk prepartum, but this practice may lead to the overconsumption of energy and increase the risk of metabolic disease postpartum. The aim of this trial was to compare the metabolic status of transition Holstein dairy cows fed a 77% forage diet (77F; NEl = 1.46 Mcal/kg; NDF = 41%) vs. those fed an 87% forage diet (87F; NEl = 1.41 Mcal/kg; 48% NDF). Approximately 60 d before calving, cows were dried off, housed in a free stall barn, and fed the 87F diet. Three weeks before expected calving, cows were randomly assigned to either the 77F treatment and switched to this diet (n = 45) or assigned to the 87F treatment and stayed on the dry cow ration until parturition (n = 42). After parturition, all cows were fed a common lactation diet (NEl = 1.59 Mcal/kg; 36% NDF). Dry matter intake was measured daily from 2 wk before to 2 wk after calving. Blood was sampled daily for 10 d postpartum. Subclinical ketosis was diagnosed using a threshold of β-hydroxybutyrate (BHBA) ≥ 1.0 mmol/L after calving. The percentage of cows pregnant and odds of being pregnant for each treatment group were determined at 60, 90, and 120 d in milk through ultrasound by the herd veterinarian. Cows on the 87F diet consumed less DM prepartum than those on the 77F diet (12.7 ± 0.3 kg/d vs. 15.4 ± 0.3 kg/d, P < 0.001), but no difference in DMI was detected after calving (19.7 ± 5.5 kg/d; P = 0.87). Although the calculated prepartum required energy intake was the same for the 2 treatments (15.3 ± 1.2 Mcal/d; P = 0.16), cows on the 77F diet consumed 4.5 Mcal/d more than those on the 87F diet (22.5 ± 0.5 Mcal/d vs. 18.0 ± 0.5 Mcal/d; P < 0.001). Postpartum concentration of BHBA was less for cows fed the 87F diet prepartum (0.49 ± 0.02 mmol/L vs. 0.59 ± 0.02 mmol/L; P = 0.02), and fewer animals on this diet were diagnosed subclinical ketosis (SCK; 49% vs. 17%; P = 0.001). Milk production tended to be less for cows fed the 87F diet prepartum (47.3 ± 0.4 kg/d vs. 48.8 ± 0.4 kg/d; P = 0.10) for the first 22 wk of lactation, which was significant for d 7 to 28 of lactation (44.6 ± 1.1 kg/d vs. 47.6 ± 1.0 kg/d; P = 0.05). Although sample size was small to draw strong conclusions on reproductive performance, at 120 d in milk, cows on the 87F diet were 0.3 times more likely to be pregnant (P = 0.03). These results indicate that feeding an 87F diet before calving can reduce rates of SCK in transition dairy cows.