Cottonseed naturally contains varying levels of gossypol dependent upon the variety of cotton and the prevailing growing conditions. Gossypol acts as a natural insect repellent within the cottonseed, and remains within cottonseed meal after oil extraction as well as in the whole cottonseed. Past research has shown that gossypol may be toxic to non-ruminants and calves, however, adult ruminants are relatively resistant due to binding of gossypol in the rumen.
Gossypol has been considered as a male contraceptive due to its negative effect upon sperm, a number of research teams (including QSML’s Dr Viv Perry) have explored this topic to find out exactly what kind of effect the consumption of cottonseed might be having on the quality of bull sperm.
What have previous studies shown?
Previous studies have shown differing effects of gossypol upon bull sperm production. Some show no effect on daily sperm production and sperm quality whilst others show an effect upon sperm abnormalities e.g. proximal droplet numbers and midpiece abnormalities. Importantly for producers, a study also reported that any damaging effects of feeding gossypol via cottonseed are reversible within one month of terminating gossypol consumption.
What did Dr Viv Perry’s research observe?
The study, run by Dr Perry and Paul Cusack for nine months in Queensland, used Hereford bulls aged between nine and 27 months of age. Half of the bulls in each of the treated and not treated group were prepubertal.The levels of Gossypol given to the bulls exceeded those in previous studies where effects upon sperm quality and daily sperm output were found.
The result showed no effects on daily bull sperm production or sperm quality.
Why were no effects reported in this study and why have previous studies differed in the observed effects upon sperm production?
Dr Perry and Paul Cusack proposed that the variation in effects may be due to the binding of the gossypol in the rumen. Gossypol is bound by many metallic minerals often found in the water sources of livestock – e.g Calcium, Iron, Sodium and Potassium. Many previous studies did not note metallic mineral consumption in feed or water source.
In the study by Dr Perry there was sufficient calcium and iron in the 55L of water drunk per bull to bind all of the gossypol in the rumen. Similarly, in a previous study which supplemented the diet with limestone – sufficient to supply 0.91% calcium to the diet – no deleterious effects were observed upon sperm quality or daily sperm output in the bull.
When feeding cottonseed to bulls
Dr Perry and Paul Cusack’s research concluded that the feeding of whole cottonseed and cottonseed meal may affect bull fertility but not if sufficient minerals are also supplied in the diet or in the water supply e.g in artesian bore water. As whole cottonseed is widely fed during the breeding season this is an important consideration for producers.
The full report is available here.