Effect of nutrition on seasonal patterns of LH, FSH and testosterone concentration, testicular mass, sebaceous gland volume and odour in Australian cashmere goats

Abstract

The effects of season and diet on LH, FSH and testosterone concentrations, testicular mass, sebaceous gland volume and male odour were examined in mature Australian cashmere goat bucks fed ad libitum with diets of low or high quality for 16 months under natural photoperiod at 29 degrees S, 153 degrees E (n = 6 per treatment). Each week plasma was sampled, the bucks were weighed, scored for male odour and assessed for testicular mass based on scrotal circumference. Each month a skin sample was taken from the occipital region for histological assessment of sebaceous gland volume. For each variable there was a clear circannual cycle that was significantly influenced by dietary treatment. In bucks fed the low-quality diet, the timing of seasonal changes in LH and testosterone concentration, sebaceous gland volume and odour score was similar, with a mid-autumn peak. In each case the high-quality diet advanced, extended the duration and increased the magnitude of the seasonal increase. FSH concentrations peaked in late spring (in bucks on the high-quality diet) or summer (in bucks on the low-quality diet), reaching a nadir in early winter. The high-quality diet significantly increased concentrations only in the last 2 months of the experiment (spring). There was no overall association between these variables and change in testicular mass; instead, it was strongly correlated with voluntary feed intake and change in body mass, themselves subject to seasonal variation with a winter or spring peak. The high-quality diet induced large increases in body mass and testicular mass during the first months of the experiment without influencing the seasonally low concentrations of FSH, LH and testosterone present at the time. These results demonstrate that the male, like the female, Australian cashmere goat, exhibits marked reproductive seasonality, and that nutrition is a powerful modulator of the seasonal cycle. They suggest that testosterone concentration, sebaceous gland volume and odour score are ultimately dependent upon LH secretion, which appears to be under strong seasonal (photoperiodic) control, with the effects of enhanced nutrition limited to periods when photoperiodic inhibition is waning. However, seasonal regulation of testicular mass, and therefore sperm production, appears to be primarily dependent on changes in voluntary feed intake and growth, with the seasonal cycle of testicular mass more a consequence of the seasonal appetite or growth cycle than of changing gonadotrophin concentrations.

Stimulation of reproductive activity in anovulatory Alpine goats exposed to bucks treated only with artificially long days

“…The increase in BW stopped in March probably due to the high levels of testosterone reached at that time (Walkden-Brown et al, 1997). In untreated bucks, the increase in BW occurred later than in light-treated males probably due to the stimulatory effect of increasing natural day length (Walkden-Brown et al, 1994;Delgadillo et al, 1999).…”

“…Testicular weight and the intensity of male odor were determined every 2 weeks (Delgadillo et al, 1991;Walkden-Brown et al, 1994). In all males, sexual behavior was observed for 20 min from 13 to 15 May, during individual tests, in which each buck was exposed to two anestrous does.…”

“…This reproductive seasonality persists in male and female Alpine goats raised in subtropical latitudes (Mohammad et al, 1984) or when subjected artificially to tropical photoperiodic variations (Chemineau et al, 1992). In Australian and Mexican bucks adapted to subtropical latitudes, the breeding season starts in late spring and ends in late autumn (Walkden-Brown et al, 1994;Delgadillo et al, 1999), while the breeding season of does of such breeds lasts from early autumn to late winter (Restall, 1992;Duarte et al, 2008). In the temperate and subtropical breeds mentioned above, photoperiod is the main environmental factor responsible for reproductive seasonality (Chemineau et al, 1988;Delgadillo et al, 2004).…”

Environmental and social cues can be used in combination to develop sustainable breeding techniques for goat reproduction in the subtropics

“…For example, Angora bucks show marked seasonal variations in their libido and testicular size with a peak in autumn (Ritar, 1991). By contrast, Australian cashmere, Damascus and Rayini male goats display a moderate reproductive seasonality (Walkden-Brown et al, 1994;Zamiri and Heidari, 2006;Ramadan et al, 2009). In cashmere goats, the breeding season, characterized by high levels of LH and testosterone, as well as the emission of a strong odor, begins in late spring and ends in late autumn (Walkden-Brown et al, 1994).…”

“…By contrast, under subtropical latitudes (238 to 408), local or adapted breeds of goats showed different annual rhythm in their sexual activity. Some breeds display large seasonal variations in their sexual activity, while others show a weak seasonality or no seasonality at all as they display sexual activity all year round (Walkden-Brown and Restall, 1996). The reproductive seasonality causes a seasonal availability of the goat-derived products (such as milk, cheese or meat), which affects both producers and consumers.…”