Reproductive performance of northern Australia beef herds. 5. Factors influencing risk of non-pregnancy

Abstract

Context Sound reproductive efficiency is a key determinant for the overall productivity and profitability of a beef breeding business. Failure of a cow to conceive results in either culling or the cost of carrying non-pregnant animals. Aims This study aimed to determine and quantify the major factors associated with non-pregnancy in commercial beef breeding herds of northern Australia. Methods A prospective population-based epidemiological study of the likelihood of non-pregnancy in cows after an annual mating in northern Australian beef breeding cows used data from 73 herds from four broad country types and 62 323 animal years; approximately 80 property-, management-group- and cow-level risk factors were considered. A multivariable model building process was employed to scrutinise the resulting dataset, so as to identify what herd management practices, nutritional, environmental, and individual cow factors were associated with non-pregnancy and estimate their magnitude of effect. Key results Non-pregnancy was disproportionately high in the Northern Forest (32.1%), compared with the Northern Downs, Central Forest and Southern Forest where it was 17.1%, 16.0% and 13.2% respectively. Time of expected calving had the largest impact on occurrence of non-pregnancy. Parity also had a significant influence, with first-lactation cows typically having 5–12% higher non-pregnancy than did mature cows. Non-pregnancy decreased with an increasing body condition score at the branding/weaning muster for lactating cows. The difference in non-pregnancy when comparing availability of wet-season pasture phosphorus content and digestibility of pasture during the dry season was 13.2 and 10.2 percentage points respectively. Conclusions This study demonstrated the substantial impact environment, herd management practices, nutrition and disease factors can have on the reproductive performance of females. Implications To optimise the efficiency of females (through reducing the occurrence of non-pregnancy) under commercial conditions in northern Australia, production systems should support beef herds calving early in the production year, being in at least moderate body condition and having access to more digestible pastures that address the nutritional requirements for both protein and phosphorus. This indicates focus for management, especially in the Northern Forest where the likelihood of non-pregnancy was highest.

Reproductive performance of northern Australian beef herds. 3. Descriptive analysis of major factors affecting reproductive performance

“…The underlying reason is most certainly that all of the prevailing risk factors within a country type combine to affect liveweight production. This was reflected in outcomes from the project where country type was a consistently significant risk factor (McCosker et al 2022a(McCosker et al , 2022bFordyce et al 2022aFordyce et al , 2022b. Although useful as a general descriptor, variation in productivity within country type across years and among specific areas is large (McGowan et al 2014).…”

“…In the Cash Cow project, adequacy of phosphorus was measured using the ratio of faecal phosphorus to estimated metabolisable energy (Jackson 2012). The threshold value of 500 mg faecal P per 1 MJ of metabolisable energy was the inflection point in the relationship between this value and cow performance (Fordyce et al 2022a(Fordyce et al , 2022bMcCosker et al 2022b). The effect of dietary phosphorus adequacy interacted with other risk factors, including cow age class, wet-season protein availability, country type and body condition score.…”

“…The most disadvantaged class of animal was first-lactation females, which have the additional challenge of maintaining condition on a skeleton that continues to grow till an average of 4.5 years of age (Fordyce et al 2013). These cattle have the highest risk of mortality, calf loss and low pregnancy rates (McCosker et al 2022a(McCosker et al , 2022bFordyce et al 2022aFordyce et al , 2022b.…”

“…The impact of 83 potential risk factors was assessed on the following: the probability of lactating cows becoming pregnant within 4 months of calving while lactating (P4M; McCosker et al 2022a); the probability of cows becoming pregnant within a 12-month cycle (Pregnant;McCosker et al 2022b); the incidence of fetal and calf loss (FCL; Fordyce et al 2022a); and the incidence of pregnant cows missing (Mortality; Fordyce et al 2022b). Candidate risk factors were initially classed as being measures of management (e.g.…”

Reproductive performance of northern Australia beef herds. 7. Risk factors affecting mortality rates of pregnant cows

“…A large epidemiological study involving commercial beef herds across northern Australia (McGowan et al 2014) was conducted to answer several questions, one of which was as follows: which measured region-, property-, management group-and animal-level risk factors are associated with pregnant females that subsequently went missing? This epidemiological research has provided the opportunity to quantify the incidence of missing cows and the impact of major risk factors.…”