Nutritional Modulation of Reproduction in Bulls
Date
2019-12-13
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Abstract
Nutrition is the single most important factor affecting reproductive development in most livestock species. The objective of this thesis was to investigate nutritional modulation of testis development at cellular and molecular level, and sperm function in bulls. In that regard, I investigated impacts of residual feed intake (RFI)- a measure of feed efficiency, early pre-natal diet and pre-pubertal diet on reproductive potential of bulls. In my first study, I investigated impacts of selection for RFI (based on sire and dam) on the reproductive potential of bull calves. Diets of pregnant cows were modulated during early gestation to determine the individual effects of diverse genetic background for RFI and pre-natal diet and the potential interaction between these variables on reproductive potential of bull calves born to them. Selection for RFI negatively impacted reproductive development of bull calves. However, there was no interaction between pre-natal diet and RFI on the reproductive development (age at puberty, SC, sperm production potential and sperm function) of bull calves. On investigating the testes of bulls with varying RFI, I found a possible role of IGF-I signaling in modulating the differences induced by RFI (age at puberty, SC and motility). To further elucidate IGF-I signaling, puberty and its associated testicular change in bulls, I utilized tissues from a differential pre-pubertal feeding study where the pre-pubertal bulls had exhibited elevated IGF-I levels and early puberty when fed a high nutrition diet (energy and protein) from 2-32 wk of life. On evaluating the testes of pre-pubertal bulls fed high vs low diet, I detected enhanced testicular cholesterol biosynthesis and Sertoli cell maturation in the high diet bulls at 16 and 24 wk respectively, with an indirect interaction between the cholesterol biosynthesis genes and the IGF-I receptor. These results suggested that IGF-I signaling is involved in Sertoli cell function. Using a cell culture model, I successfully tested this theory and was able to prove its role in promoting cholesterol biosynthesis. When evaluating the post-pubertal testes of bulls fed differential pre-pubertal nutrition, I detected upregulated mitochondrial function both in the testes and sperm of high diet fed bulls and proposed this as a mechanism to support their greater sperm motility, sperm production potential and enhanced cholesterol biosynthesis. Considering impacts of our dietary modulation on mitochondrial function and its potential involvement in epigenetic regulation, I evaluated the sperm epigenome and detected differential methylation mainly in genes implicated in spermatogenesis, sperm function and early embryo development. To conclude, the results of my thesis offer further confirmation to the AI industry about the benefits of allocating higher nutrition to bulls during their early post-natal life. Nutritional modulation has also been validated as an effective model to study male reproductive development.
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Keywords
Nutrition, Reproduction, Testes, Bull
Citation
Johnson, C. T. (2019). Nutritional Modulation of Reproduction in Bulls (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.