Persistent selection for fecundity increases milk production in inbred Quackenbush (OQS5) mice : a potential model for the discovery of genes regulating lactation. (Abstract)

Abstract

10A Persistent selection for fecundity increases milk production in inbred Quackenbush (IQS5) mice: a potential model for the discovery of genes regulating lactation Z. Muhammad, P.C. Wynn, P.C. Thomson and P.A. Sheehy Collaborative Research Centre for Innovative Dairy Products, Faculty of Veterinary Science, University of Sydney, PMB 3, PO Camden NSW 2570 mzub0222@mail.usyd.edu.au The biosynthetic capacity of the mammary gland is all important in determining production efficiency in the dairy industry. This trait is responsive to quantitative genetic selection, but we have been unable to elucidate the pool of important genes responsible for improved milk output. We are using two lines of mice to assist with this process. We report here on the characterization of the lactational performance of 2 inbred strains of mice that differ greatly in fertility. Dams of the 2 strains, the IQS5A and CBAA, were mated and upon pupping, litters were normalised to a maximum of 12 pups (range 912) and 6 (range 36) pups for the two lines respectively. Dams were offered ad libitum a soluble high energy glucose based diet (high glycaemic index: Higgins et al. 1996) and housed at 21oC in a 12:12 (light:dark) lighting regimen. Milk production was assessed using a weigh suckleweigh technique in which differences in pup bodyweight over a suckling period (2 h) following a 4 h separation of pups and dams was estimated over 24 h (commencing at 0000, 0600, 1200 and 2400h daily) for 18 days postpartum. Litters were left undisturbed for the first day so as not to disrupt colostrum intake. Litter liveweight gain in each 2 h suckling period was corrected for metabolic loss assessed during the 4 h period of separation. Dam weight (W), feed intake and total litter liveweight were recorded daily in addition to estimates of milk synthesis (Table 1). Lactation curves were constructed for each strain and the mean (� SD) data analysed by unpaired t test. Peak milk yield was reached on days 10 and 14 for IQS5 and CBA mice respectively. The significantly greater milk output from IQS5 mice is associated with an earlier peak in the lactation curve with a greater efficiency of partitioning of nutrients into milk in this genotype. This latter observation is based on the similar feed intake per unit of dam W in the two strains. Despite the highly variable demands of lactation dam, liveweight was conserved in both strains over the course of the lactation (W for IQS5 and CBA dams respectively at day 1 were 40.8 � 1.5 g and 23.5 � 1.8 g, and at day 18 were 39.8 � 1.2 g and 26.7 � 2.3 g). The lactational performance of these mouse strains diverges sufficiently to provide a basis for studies of differential gene expression between key metabolic tissues to elucidate mechanisms associated with the superior lactational performance of the IQS5 strain. Elucidation of these genes will provide the scope for the identification of polymorphisms potentially useful in quantitative genetic selection programs used in the dairy industry. IQS5 and CBA mice were provided by Associate Professor Chris Moran and Dr Ian Martin. Higgins, J.A., Brand Miller, J.C. and Denyer, G.S. (1996). Journal of Nutrition 126, 596602. Table 1 Milk production and feed efficiency in the two mouse genotypes (*P<0.05). Total milk production (g) * 83.5 � 5.14 29.8 � 6.68 Total feed consumption (g) * 272.7 � 23.4 158.0 � 14.9 Total growth (g) * 5.17 � 0.20 4.46 � 0.97 Milk production (g/d) /g dam W* 0.114 � 0.005 0.064 � 0.018 Milk production (g/d) /g feed * 0.308 � 0.040 0.179 � 0.055 Feed intake (g)/d per g dam W 0.368 � 0.030 0.334 � 0.073 Strain IQS5 CBA Recent Advances in Animal Nutrition in Australia, Volume 14 (2003)