Discipline: reproduction; Keywords: SA Holsteins, stillbirth, EBV’s, genetic evaluation, environmental effects.
Stillbirth remains a problem in dairy herds in many countries and is increasingly included in national breeding objectives. In South Africa, however, we lack reliable information on the incidence of stillbirth that can be used to improve this trait genetically. Currently, there are no estimated breeding values (EBVs) for any measures of calving performance produced under the national genetic evaluation programmes. The aim of the study by the authors cited below was therefore to assess the incidence of stillbirth and determine environmental factors affecting the trait in South African Holstein cattle.
The data set consisted of 13 143 calving records of 7 723 cows, from 41 herds, recorded under the National Dairy Animal Recording and Improvement Scheme between 2014 and 2018. Data were statistically analysed using the PROC FREQ and General Linear Models (GLM) procedures of SAS 9.4: 2016. Environmental effects tested for their influence on stillbirth were herd-year-season (HYS) of calving, sex of calf and parity.
Live calves represented 93.6% of the animals born and 6.38% of the calves were born dead. Herd-year-season, calf sex, and parity all had a highly significant (P<0.0001) effect on stillbirth, in agreement with various other studies elsewhere. The frequency distribution of stillbirth for first, second and third calvings was 8.72%, 4.38% and 5.47%, respectively. Increased rates of calving difficulty at first calving, relative to later calvings, is a widely found, and is believed to be the cause of higher incidences of stillbirths. Calving year followed calving number as the next most important factor affecting stillbirth. Cows which calved in the year 2014 had the highest incidence of stillbirth (8.26%) and 2018 had the lowest incidence of stillbirth (4.54%). There was a general decline in incidence of stillbirth from 2014 to 2018, which may partly be a reflection of biological variation within the population over time. Cows calving in autumn had the highest incidence of stillbirth (7.16%) and those calving in winter had the lowest (5.82%). Male calves had a higher incidence of stillbirth (8.48%) compared to females (4.41%), as widely reported in the literature.
The incidence of stillbirth in South African Holstein cattle observed in the study is slightly lower than those observed elsewhere. This might be due to under-recording of stillbirth by South African farmers. Herd-year-season of calving, calving number and calf sex were significant sources of variation in stillbirths. These factors should be included in statistical models for the genetic analysis of stillbirth in the South African Holstein cattle population.
M.P. Ratshivhombela, B. Dube, O. Tada, M.A. Madilindi & C.B. Banga, 2019. An analysis of incidence of stillbirth in South African Holstein cattle.In: Proc. of the 51st Annual Congress of the SASAS, Bloemfontein, 10-12 June 2019, Abstract 168.