Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 9, 2013
Publication Date: July 1, 2013
Citation: Lents, C.A., Rempel, L.A., Klindt, J., Wise, T., Nonneman, D., Freking, B.A. 2013. The relationship of plasma urea nitrogen with growth traits and age at first estrus in gilts. Journal of Animal Science. 91(7):3137-3142. Interpretive Summary: Gilts that reach puberty at an earlier age with more backfat have greater lifetime productivity; however, producers do not have a reliable means of selecting gilts that will reach puberty early because investigations into the relationship of age at puberty with discrete measures of body fatness or weight have not yielded consistent results. The timing of the onset of puberty in pigs is thought to be related to metabolic state, which reflects accretion of fat and lean tissues. Scientists measured concentrations of plasma urea nitrogen (PUN), a blood metabolite that indicates the efficiency of use of amino acids for lean tissue growth, at different ages throughout development. They found that gilts with greater concentrations of PUN measured at 145 d of age were fatter and reached puberty earlier than gilts with lesser concentrations of PUN. There was no association with puberty when PUN was measured at younger ages. Because PUN is a heritable trait, these results indicate that PUN could be measured at young ages to select animals with greater efficiency of amino acid use and lean tissue growth, allowing producers to increase profitability and reduce nitrogen excretion into the environment without negatively impacting pubertal development of replacement females. Furthermore, measuring PUN at older ages could allow producers to discriminate between gilts that would have more favorable performance for breeding purposes and those that would do better in finishing units. The impact that such a selection strategy has on lifetime productivity of replacement gilts, however, remains to be determined.
Technical Abstract: Gilts that reach puberty at an earlier age with more backfat have greater lifetime productivity. Increased growth rates generally promote earlier age at first estrus; however, an association of age at first estrus with discrete measures of body fatness remains controversial. We tested the hypothesis that metabolic state as determined by concentrations of plasma urea nitrogen (PUN), which reflect lean tissue growth, were correlated with age at first estrus. Blood samples were collected from gilts (n = 337) at 102, 123, and 145 d of age during development. Concentrations of albumin, creatinine, glucose, and PUN were determined. Body weight and backfat thickness were determined at each time point. From 130 to 240 d of age, gilts were monitored for first pubertal estrus. Concentrations of creatinine increased whereas concentrations of glucose decreased with increasing age (P < 0.0001). Concentrations of albumin and PUN remained relatively stable throughout development. Average daily BW gain (r = 0.22) and change in backfat thickness (r = 0.29) had a positive phenotypic correlation (P < 0.0001) with PUN at 145 d of age. Concentrations of PUN at 102 and 123 d of age were not phenotypically correlated with pubertal age, but there was a moderately negative phenotypic correlation (r = –0.22; P < 0.0001) of PUN at 145 d of age with age at first estrus along with a negative genetic correlation (r = –0.42). The relationship of PUN with age at first estrus shifted from liner to quadratic with advancing age. These data demonstrate that near the age at which gilts are selected for entry into the breeding unit, those with greater PUN have increased BW and backfat thickness and display pubertal estrus earlier but that PUN does not account for additional variation in age at first estrus beyond growth rate or backfat. It is concluded that PUN can be used to select gilts with increased efficiency of nutrient use without negatively impacting pubertal development.