Fetal programming in cattle: the effects of varying maternal protein intake in adolescent beef heifers on fetal and postnatal growth and development of the calf

Numerous studies, including those in agriculturally important species, have shown that maternal nutritional status during gestation influences the fetal development, postnatal growth pathways and metabolism and reproductive development of the offspring. Wide variation in pasture quality and quantity available for the cow herd throughout the breeding season and during gestation is common in extensive grass-fed beef production systems. In the northern Australian rangelands, protein, rather than energy, is the major limiting nutrient for cattle in dry-season pastures with protein supplementation of breeding heifers an animal husbandry requirement. Few studies in cattle have specifically evaluated the effects of maternal protein restriction and/or supplementation on the fetal and postnatal development of the offspring. This thesis investigates the effect of low and high protein intake in nulliparous beef heifers during the peri-conception and first trimester of gestation upon feto-placental growth and the subsequent postnatal growth and reproductive development of the male offspring. Furthermore, the impact of maternal nutrition on appetite, feedlot performance and carcass traits was evaluated in the male offspring. The outcomes of the first three chapters of this thesis highlight the importance of the peri-conception period and first trimester upon fetal and placental development. We have demonstrated that protein restriction (125 % versus 70 % of requirement) during the peri-conception period and first trimester decreased early fetal growth in the bovine in a sex-specific manner in association with maternal endocrine perturbations, and may contribute to early embryonic loss. Furthermore, we show that protein restriction during the peri-conception period and first trimester alters placenta parameters and produces asynchronous organ development in the bovine by 98 days post-conception. After feeding to meet nutritional requirements (but not realimentation) during the second and third trimester, the observed differences in fetal and gross placenta parameters measured at 98 days post-conception were not present at birth. Intriguingly, the sex-related differences apparent at 98 days post-conception and normally observed in birth weight in the neonate were disrupted. This suggests sex- specific catch-up growth to term dependent upon early gestational dietary treatment. We propose that placental adaptations and an accelerated growth response in the restricted female fetus reduced the observed differences in fetal weight apparent at 98 days post-conception after the nutritional treatment ceased, thereby disrupting the normal disparity in birth weight between heifer and bull calves. However, as indicated by the differing fetal organ measures at the end of the first trimester, similarity in birth weight does not preclude that developmental programming of the structure and/or function of the fetal organs and tissues has already occurred following nutritional stress in early gestation. On the contrary, prior studies have shown that birth weight is not a satisfactory indicator of intrauterine growth restriction and that suboptimal maternal nutrition may have lasting effects on the post-natal growth and development and health of the offspring. The second component of this study, which forms the final two chapters of the thesis, examined the post-natal growth and reproductive development of the non-castrated male offspring through to slaughter at 598 days of age. We demonstrated in the developing bull, that low dietary protein during the peri-conception period lowered sperm quality parameters during pubertal development with a concomitant delay in age of puberty. These effects were subsequent to lower FSH concentrations in this low peri-conception group. The circulating hormone data suggest that the peri-conception diet may have altered the development of the hypothalamic–pituitary-gonadal axis and the corresponding receptivity to circulating hormones. These male offspring underwent a 70-day residual feed intake feedlot test commencing at 528 days of age. Offspring from heifers that had a change in diet at the end of the peri-conception period from high protein to low protein, and visa versa, had 9% daily higher feed intake on test than offspring of mothers that remained on a constant low protein diet throughout the peri- and post-conception period. Offspring liveweight, feed efficiency and carcass weight were not different among bulls, however dressing percentage, estimated retail beef yield and eye muscle (longissimus dorsi) area were all lower in offspring of heifers fed a low protein diet during the first trimester. Significantly, these findings on the sex-specific effects of peri-conceptional dietary perturbations in cattle represent the first such data in a mammalian species with ovary structure, embryonic development and gestational length similar to the human. In combination, this work represents the first study to highlight the importance of maternal dietary protein intake during the peri-conception period and first trimester upon fetal and postnatal development in beef cattle. In a pasture-based production system where variation in feed quality through breeding and gestation occurs, quantification of these effects upon long term productivity of the progeny and elucidation of the causal mechanisms remains an important area of study.

Author dc:creator

• Copping, Katrina Joan

Advisors dc:contributor.advisor

• Perry, Vivienne
• Rodgers, Ray

• Research by publication
• cattle
• fetal programming
• maternal dietary crude protein

Handle dc:identifier.uri

http://hdl.handle.net/2440/114261

OAI identifier oai:identifier

oai:digital.library.adelaide.edu.au:2440/114261