Pre-conception nutrition estimated from milk composition characterises the sex ratio of offspring in cattle.

In livestock breeding, offspring of a particular sex are often favoured. Various biological mechanisms influence the offspring sex ratio (OSR). It has been hypothesised that maternal body condition/nutritional status influence OSR. We analysed the relationship between the nutritional status of the cow and OSR. The analysed dataset contained 40,913 milk recordings of 39,192 cows from 3625 farms. Nutritional status was estimated based on the fat-to-protein (F:P) ratio and urea content in milk in the seven to fourteen days prior to conception. Somatic cell count (SCC) was also considered. Cows with > 150,000 SSC were analysed separately. When SSC was normal (≤150,000), high urea with high F:P resulted in a higher probability of male offspring (61 %), with OSR significantly deviating towards male (1.47). Conversely, a high urea level and low F:P resulted in a higher probability of female offspring (57 %), with OSR significantly in favour of females (0.79). At normal or low milk urea, the sex of the offspring did not change within F:P classes. The sex ratio did not deviate from 1:1 when F:P and urea were in the normal range. When SCC was high, the probability of particular sex did not change significantly in either combination of F:P and urea, but OSR showed a tendency toward males (OSR>1) when F:P and urea were low or normal. Our results confirmed the influence of maternal nutritional status on the offspring sex. Thus, adjusting nutrition in the pre-insemination period seems to be a way to influence the sex ratio of offspring in dairy cows.