Researchers in New Zealand recently set out to see whether you can influence the ratio of male-to-female calves by altering the feed allowance of lactating dairy cows around the time of conception. The study was published in the November Journal of Dairy Science.
Using 770 cows on two farms, the scientists followed two groups of cattle that received different access to feed during the first 14 days of a seasonal breeding program. The first group featured 453 cows that were given unlimited access to pasture. The second group, 317 cows, had restricted access to pasture.
These cows had lower milk yields and it took three to four weeks for them to recover milk production.
Results show that there was no detectable difference in birth sex ration between the two groups of cows following a short-term feed restriction around the time of conception.
However, the researchers did find associations between pre-calving body condition, negative energy balance, milkfat-to-protein ratio and birth sex ration. These associations predicted a greater proportion of male calves born to cows that calved in lower body condition, cows gaining body condition from calving to mating, and cows with lower milkfat-to-protein ratios.
These findings suggest that the timing of the negative energy balance — relative to conception — may be important.