Performance of Mouse Lines Divergently Selected for Heat Loss When Exposed to Different Environmental Temperatures. II. Feed Intake, Growth, Fatness, and Body Organs

Mouse populations differing in metabolic rate have been developed through selection for high (MH) and low (ML) heat loss, along with the unselected controls (MC). Objectives of the study were to compare the MH, ML, and MC lines for feed intake, growth, body fatness, and organ weights when reared at 12, 22, and 31°C, and investigate potential line × environment interactions. Feed intake was recorded weekly from 3 to 9 wk of age, and BW at 3, 6, and 9 wk of age. Body fat percent and organ weights were measured at 9 wk of age. No line × environment interactions were detected for any of the traits measured. The MH mice consumed more feed than ML mice from 5 to 9 wk of age. Between 8 and 9 wk of age, MH mice consumed 13% more feed than the ML mice, but they were relatively leaner (14.45 vs. 16.32% body fat); MC mice were intermediate for both traits. Mice in the cold environment consumed the greatest amount of feed, and those in the hot environment consumed the least. Males consumed more feed than females, and the difference was greater in the cold than in the hot environment. No differences in BW were found between the lines. Mice in the 22°C environment were heavier than their age-matched counterparts in the other two environments, and males were heavier than females at all ages. Relative to BW, the three lines had similar tail length, body length, and liver weight. Mice in the cold environment had heavier spleens and livers than those in the hot environment but relatively shorter bodies and tails; the normal environment was intermediate for these traits. Results from this study indicate that selection to decrease maintenance requirements did not produce mice with any less ability to grow and perform under an array of environmental temperatures

Performance of Mouse Lines Divergently Selected for Heat Loss When Exposed to Different Environmental Temperatures. I. Reproductive Performance, Pup Survival, and Metabolic Hormones

Mouse populations differing in metabolic rate have been developed through selection for high (MH) and low (ML) heat loss, along with the unselected controls (MC). Objectives of the study were to compare the MH, ML, and MC lines for reproductive performance, pup survival, and metabolic hormones when reared at 12, 22, and 31°C, and to search for line × environment interactions. Conception and litter size were recorded on the parent generation mice introduced to the environments at 11 wk of age and bred after a 3-wk acclimatization period. Survival of pups (pre-weaning to 3 wk; post-weaning from 3 to 9 wk of age) was measured with continuous exposure in the designated environment from birth to the time of measurement. Corticosterone, triiodothyronine (T3), and thyroxine (T4) serum concentrations were measured on the parent generation after producing litters and on the pup generation at 9 wk. No line × environment interaction was detected for conception rate, preweaning mortality, postweaning survival, pup weaning weight, or body temperature. There were no differences in conception rate among lines and environments. Environments affected survival of pups, but there were no line differences. Rectal body temperatures were greater for MH than ML mice, and MC mice were intermediate; body temperature of mice did not differ among the environments. Lines differed significantly in litter size only in the 22°C environment. No significant line differences were found for serum corticosterone or serum T3 or T4. Line × environment interaction was detected only for litter size and for serum corticosterone concentration in dams. Contrary to the other two lines, ML dam performance relative to MH and MC was not affected negatively by either of the thermal environments. Results from this study do not raise concern that selection to decrease maintenance requirements will produce livestock with any greater liability to cope and perform under an array of environmental temperatures

Application of a sex identification technique in juvenile ostriches and its potential application in Botswana

Sexing ostrich chicks and juveniles before the dimorphous appearance of the plumage that starts at 14 months of age is proving difficult and cumbersome for Botswana farmers. This problem delays early selection of birds for breeding and trading. It also means that birds are often sold as a mixture of males and females. DNA-based sex identification provides a solution and is amenable to large-scale application. The application of the multiplex polymerase chain reaction (PCR) was used to determine the sex of 6-months old juvenile ostriches. The blood from four mature males and four mature females were used to verify the assay. The test group consisted of 19 randomly selected six-month old birds, which turned out to be 10 males and nine females. The PCR technique uses two pairs of primers. The primers SS1 and SS2 amplify a 650 base pair (bp) female-specific fragment, while the primers L014a and L014b amplify a fragment about 280 bp, from both sexes. The females were thus distinguished by amplification of two bands after agarose gel electrophoresis, and the males by one band. Following the successful application of this technique using DNA extracted from blood, further investigations have to be conducted, using DNA extracted from other body tissue samples such as feathers or skin. A scenario is envisaged whereby, during tagging of the chicks, a body tissue sample such as a blood feather could be sent to the laboratory for DNA sexing. This technique would aid farmers in identifying the sex of their birds at a young age. South African Journal of Animal Science Vol.32(3) 2002: 160-16