Reducing the number of critical transitions for dairy cows: effects on milk yield and health

Drying-off, calving, and start of lactation are critical transitions for a dairy cow. By extending the voluntary waitingperiod for insemination (VWP), calving interval (CI) is extended, reducing the number of transitions per year, withpossible positive effects for health. The risk of increased CI is a reduction in milk yield per year, as there are less peaksin milk. This study investigated effects of extended VWP on milk yield, body condition, and disease incidence. Cows(n=150) within one herd were blocked for parity, calving season, expected milk yield and persistency, and 6 weeks aftercalving within blocks randomly assigned to one of three VWP (50, 125, or 200 days), and monitored for a completelactation. Fat-and-protein-corrected milk yield per day (FPCM), body weight, and BCS were analysed for the first 40weeks in lactation and for the last 12 and 6 weeks before dry-off, using a repeated measurements model with fixedeffects of VWP, parity (1 or 2+), time, and interactions, and cow as repeated subject. Milk yield was also calculatedas FPCM per day of CI. Mean CI was 393, 457, and 503 days, for VWP50, VWP125, and VWP200, respectively. Inthe first 40 weeks in lactation, FPCM was not affected by VWP for parity 1, while for parity 2+ FPCM was lower inVWP200 compared with VWP125 or VWP50 (32.7 vs 35.6 vs 34.9 kg/day, P<0.10). FPCM per day of CI was notaffected by VWP for parity 1, while for parity 2+ FPCM per day of CI was lower in VWP200 compared with VWP125or VWP50 (23.5 vs 26.5 vs 27.1 kg/day, P<0.05). In the last 6 weeks before dry-off, FPCM was greater for VWP50compared with VWP125 or VWP200 for parity 2+ (20.3 vs 17.2 vs 14.7 kg/day, P<0.05). In the last 12 weeks beforedry-off, for parity 2+, BCS was greatest for VWP200, intermediate for VWP125, and smallest for VWP50 (3.5 vs3.0 vs 2.6, P<0.05). Extending VWP for heifers did not affect milk yield, but cows with a 200 d VWP had a reducedmilk yield per day and less milk before dry off. Extending VWP for cows could increase fattening in late lactationcompared with a VWP of 50 days.