Advances in bovine theriogenology in New Zealand. 1. Pregnancy, parturition and the postpartum period

Abstract

Unique systems of breeding and calving management have been developed to allow New Zealand cattle herd owners to maintain seasonally concentrated calving patterns. Improved pastures are used as the sole ration for most beef and dairy cows with limited conservation and no grain feeding. Patterns of calving are described in relation to herd Planned Start of Calving (PSC) dates, calculated as 282 days after the fi rst date of insemination in the preceding seasonal artifi cial breeding (AB) programme. Corticosteroids have been systematically used in over 80% of New Zealand dairy herds to induce premature parturition (calving induction) during the third trimester of pregnancy for about 25 years, to condense calving patterns into periods of 6-12 weeks. Widespread use of calving induction has minimised the adverse effects of declining reproductive performance in dairy herds on the sustainability of seasonally concentrated calving. The use of calving induction is now discouraged on animal welfare grounds and due to possible consequences for the marketing of New Zealand dairy products.Recent declines in the reproductive performance of dairy herds are linked to increased prevalence of extended periods of postpartum anovulatory anoestrus (AA), which has become the major form of infertility in dairy herds in New Zealand and can be related to reliance on grazed pasture as the sole diet for cows of increasing genetic merit. The prevalence of AA is infl uenced by parity, breed, recent genetic origin within a breed, body condition score, herd and year. Management strategies such as oncedaily milking, preferential grazing or feeding of silage, have not proven as successful as hormonal treatments.Although seasonally concentrated calving has remained a standard feature of the industry's low-cost, pasture-based system of management, continuing research will be required to economically maintain this pattern.

Use of herd management programmes to improve the reproductive performance of dairy cattle

“…Many of the reproductive performance measures used as key performance indicators for year-round calving (Fetrow et al, 1988) are inappropriate for seasonal calving systems (Macmillan, 2002;Morton, 2010). For example, in year-round calving systems indices such as calving to first insemination or calving to conception are commonly analysed, whereas in seasonal calving systems cows are bred upon oestrous detection after a calendar date, set as the start of the seasonal breeding programme, irrespective of the interval after calving of individual cows.…”

Using a whole farm model to determine the impacts of mating management on the profitability of pasture-based dairy farms

“…High levels of reproductive performance are required in seasonal dairying where inter-calving intervals are constrained to 365 days (Macmillan, 2002a). Mating management is central to reproductive performance of seasonally mated dairy cattle herds.…”

Postpartum anoestrus in five seasonally‐calving dairy farms in Victoria, Australia

“…1 Delays in the start of ovulation and expressions of oestrus can affect submission rates early in the mating period, resulting in suboptimal herd-level reproductive performance. 3,4 After calving, cattle may undergo a period of postpartum anoestrus before they resume overt cyclicity. These animals are less profitable because of reduced production and a decreased probability of pregnancy.…”

“…5 In seasonally-calving dairy production systems dairy cattle are described as being in a state of no visible oestrus (anoestrus) when they have not been detected in oestrus shortly before the herd MSD or during the mating period. 8 Anoestrous cows are more likely to have longer calving to first-service intervals, 9 longer calving to conception intervals, 3,9 lower conception rates 6,10-12 and lower overall pregnancy rates compared with those that have resumed cyclicity. 2,7 Cows diagnosed as being anoestrus may have ovulatory or anovulatory anoestrus, or ovarian pathology.…”

“…These animals are less profitable because of reduced production and a decreased probability of pregnancy. 3,4 After calving, cattle may undergo a period of postpartum anoestrus before they resume overt cyclicity. 5 In seasonally-calving dairy production systems dairy cattle are described as being in a state of no visible oestrus (anoestrus) when they have not been detected in oestrus shortly before the herd MSD or during the mating period.…”