Voluntary waiting period
InCalf's messages
The InCalf Book recommends that reproductive performance be assessed from calving using the 100-day in-calf rate and 200-day not-in-calf rate in year-round calving herds. A long gap between calving and when the cow is first mated will reduce reproductive performance in year-round calving herds. Shorter voluntary waiting periods result in higher 100-day in-calf rates and lower 200-day not-in-calf rates, although semen use may be increased. See pages 145-147, and page 27 of The InCalf Book.
What the current scientific literature says
In year-round calving herds, where reproductive performance is assessed by measuring the rate at which cows get pregnant following calving, increased voluntary waiting periods reduce reproductive performance substantially. In seasonal calving herds, where reproductive performance is assessed by measuring the rate at which cows get pregnant following the commencement of mating, increasing the interval from calving to mating start date increases reproductive performance.
Reproductive performance can be assessed from either mating start date or from calving. Effects of varying voluntary waiting periods depend on which approach is used.
Where reproductive performance is assessed from mating start date, increasing voluntary waiting periods up to 100 days (ie increasing the interval from calving to mating start date) substantially increases reproductive performance. Effects of increases over 100 days on reproductive performance are not consistent - see Calving to mating start date interval WebTECH page.
In contrast, where reproductive performance is assessed from calving rather than from mating start date, increased voluntary waiting periods reduce reproductive performance substantially. Although voluntary waiting period was only weakly associated with time to conception in an observational study (Ferguson 1996), much larger effects are reported from intervention studies where cows were randomly allocated different voluntary waiting periods. Prolonging the voluntary waiting period to 74 days (Whitmore et al 1974), 80 days (Schneider et al 1981), 120–150 days (Schindler et al 1991) 140 days (Ratnayake et al 1998; Larsson and Berglund 2000; Osterman and Bertilsson 2003) or 150 days (van Amburgh et al 1997) increases mean calving to conception interval substantially.
These adverse effects of increased voluntary waiting period reflect the combination of:
- increases in conception rates in association with increased calving to service intervals and
- prolonged time from calving to first service in delaying conception.
Conception rates are strongly associated with calving to service interval. Numerous studies have reported low conception rates to services soon after calving, with higher conception rates occurring between 100-200 days after calving (Arnott 1961; Whitmore et al 1974; Williamson et al 1980; Berger et al 1981; Dohoo 1983; Hillers et al 1984; Reimers et al 1985; Ferguson 1991; Hodel et al 1995; Ferguson 1996; Thompson et al 1996; Dransfield et al 1998; Royal et al 2000; Mayne et al 2002). This relationship seems curvilinear, with largest incremental increases in conception rate occurring sooner after calving. Smaller increases are reported after day 40 (Stevenson et al 1983). These increases in conception rate are similar amongst both clinically healthy cows and cows diagnosed with various diseases in early lactation (Dohoo 1983) but may be larger where negative energy balance in early lactation is more extreme (Ferguson et al 1989) and amongst multiparous cows (Schindler et al 1991). Longer calving to service intervals are associated with increased likelihood of one or more pre-mating ovulations (Macmillan and Clayton 1980; Stevenson and Call 1983; Senatore et al 1996) as well as increased time from calving per se and both components may act independently to cause the positive relationship between calving to service interval and conception rates (Macmillan and Clayton 1980). Time from calving to service is directly associated with conception rates as well as indirectly via metabolic risk factors (Moss 2001), suggesting that correcting nutritional factors may reduce but not eliminate this relationship. Lower conception rates following insemination soon after calving are due in part to increased risk of embryonic mortality (Ball and Morant 1978).
These beneficial effects of longer voluntary waiting period on conception rates are outweighed by delays in conception due to prolonged time to first service. In observational studies, longer intervals from calving to first service are associated with longer intervals to conception at both cow- (Williamson et al 1980; Dohoo 1983; Stevenson et al 1983; Etherington et al 1985; Gaines et al 1993) and herd- (Ouweltjes et al 1996; Rougoor et al 1997) levels. Conception rates are not always increased following prolonged voluntary waiting periods (Schneider et al 1981; van Amburgh et al 1997). However even where conception rates are higher amongst cows allocated to longer voluntary waiting periods, mean calving to conception intervals are still increased substantially (Whitmore et al 1974; Schindler et al 1991; Ratnayake et al 1998). Accordingly herd managers have been advised to avoid prolonged voluntary waiting periods (Fetrow 1993) unless extended lactations are desired. Managers have also been advised to avoid short voluntary waiting periods (less than 50 days) due to reductions in both conception rates and potential reductions in annual milk yield per cow (Esslemont 1979; Ministry of Agriculture Fisheries and Food 1984).
Compiled by Dr John Morton
References
Arnott WJ (1961) Problems of artificial breeding of cattle. Australian Veterinary Journal 36: 140-145
Ball PJH and Morant SV (1978) Factors affecting the incidence and timing of embryo losses in dairy cattle. Animal Production 26: 357-358
Berger PJ, Shanks RD, Freeman AE and Laben RC (1981) Genetic aspects of milk yield and reproductive performance. Journal of Dairy Science 64: 114-122
Dohoo IR (1983) The effects of calving to first service interval on reproductive performance in normal cows and cows with postpartal disease. Canadian Veterinary Journal 24: 343-346
Dransfield MBG, Nebel RL, Pearson RE and Warnick LD (1998) Timing of insemination for dairy cows identified in estrus by a radiotelemetric estrus detection system. Journal of Dairy Science 81: 1874-1882
Esslemont RJ (1979) Management with special reference to fertility, EAAP publication no. 25. In: Swan H and Broster WH (Editors), Feeding strategy for the high yielding dairy cow. Granada, London, pp 258-294
Etherington WG, Martin SW, Dohoo IR and Bosu WTK (1985) Interrelationships between ambient temperature, age at calving, postpartum reproductive events and reproductive performance in dairy cows: a path analysis. Canadian Journal of Comparative Medicine 49: 254-260
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Ministry of Agriculture Fisheries and Food (1984) Dairy herd fertility, Reference book 259. Her Majesty's Stationery Office, London
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