Proof that BCS lifts fertility

Coverage from a recent genetics field day at Kepler Station, the South Island site of the Informing NZ Beef across-breed beef progeny test.

In Livestock8 Minutes

Results from a five-year beef progeny test show that body condition is a heritable trait and there is a strong correlation between cow body condition and reproductive performance.

As part of her PhD, agricultural scientist Franzi Weik has been analysing the data set collected from the five large-scale beef operations that participated in Beef + Lamb New Zealand’s beef progeny test between 2014 and 2019.

Speaking at the recent B+LNZ Genetics field day at Kepler Station (South Island site of the Informing NZ Beef across-breed beef progeny test), Weik says she looked at the phenotypical and genetics influences on body condition and the relationship between body condition score (BCS) and pregnancy.

The cows in the progeny test were weighed and body condition scored three times a year – at mating, weaning and calving. They went through an artificial insemination programme followed by two cycles of natural mating.

Weik says to optimise conception, the breeding cow needs to be at a BCS of seven at mating. Beyond that there was no benefit in terms of conception rates, but there was a penalty in reproductive performance from having cows at a BCS below seven.

Identifying low condition cows and preferentially feeding them before calving so they can reach a BCS of seven would help improve reproductive performance at the next mating. This not only increases conception rates, conception happens earlier which helps tighten up the calving pattern.

“The most value will be obtained by reducing the number of low conditioned cows in the herd,” Weik says.

As a rule of thumb, 27kg will shift the BCS by one unit in Angus and Hereford cows.

Weik says genetics are an additional tool that could be used to help the breeding cow herd maintain condition and get back in calf. BCS has a heritability of 27% so the right genetics could help lift the BCS of the entire herd by up to one BCS.

“There is potential to identify sires with high genetic merit for BCS, but at the moment we don’t have EBVs for BCS to include in our bull selection.”

As part of her research, Weik looked at the relationship between cow BCS and fat measurements. While EBVs for fat are valuable from a finishing point of view, they are a blunt instrument when it comes to helping lift BCS in breeding cows.

She says rib fat EBVs are an important tool for finishers to help them achieve industry targets of 3–10mm fat, but they are not good indicators of body energy reserves in cows.

Unfortunately, positive fat EBVs are the only tool farmers have in the toolbox, but they should be used primarily to improve the performance of the finishing herd.

The progeny test highlighted the big fluctuations in weight many breeding cows experience over the course of a year.

Weik says there were big differences between farms and while this could be management and seasonally related, it showed how inter-related liveweight, BCS and reproductive performance are.

Progeny test in third year

This spring, the third crop of calves born into Beef + Lamb New Zealand’s Informing New Zealand Beef Progeny Test will hit the ground on Pamu’s Kepler Farm.

Anna Boyd, Beef + Lamb New Zealand genetic operations specialist – beef, says 405 Hereford and Angus cows were artificially inseminated (AI) at the Manapouri farm last December, using genetics from six Angus, six Hereford bulls and one internationally sourced Angus bull. The AI programme was followed up by farm-selected bulls.

Boyd says despite the dry spring, the cows were in very good condition going into mating and this was reflected in the pregnancy test results in March. The re-bred 2020-born heifers went to the bull at a body condition score (BCS) of 7.6 and had a 69% success rate to AI. The 2019-born females went to the bull at an average BCS of 7.5 and had a 63% in-calf rate to AI.

Last spring, the first heifers sired by progeny test sires (born in 2021) went to the bull for a natural mating. Weighing an average 421kg going into mating, they had a pleasing 96% pregnancy rate.

This breeding information will be amongst the data gathered on the heifers’ fertility traits which will include days to conception. Using foetal ageing, this is calculated to within five days of conception.

Along with steers born the same year, the heifers were structurally assessed and had their eye muscle area, rib fat, rump fat and intramuscular fat ultrasound scanned and measured.

The 2021-born steers will all be processed at Silver Fern Farms’ Finegand plant by late June and carcase data, including Beef EQ data, will be collected and analysed.

Boyd says in April, the second cohort of progeny test calves born on Kepler were weaned and docility scored.

Taupo’s Lochinver Station came into the progeny test last year and had their first mating in January.

Boyd says 586 Angus cows went through an AI programme using the same Hereford and Angus genetics used at Kepler, with the addition of four Simmental bulls. Pregnancy testing showed a 58% success rate to AI.

The seven-year Informing New Zealand Beef (INZB) programme is a partnership between Beef + Lamb New Zealand, the Ministry for Primary Industries and the New Zealand Meat Board. It aims to boost the sector’s profits by $460m over the next 25 years.

Focused on increasing uptake of the use of high-quality genetics in the beef industry, the four main components of the programme are developing New Zealand-specific breeding indexes, building a genetic evaluation and data infrastructure, running progeny test herds, and developing new data sources.