Past studies guide future research
04 January 2016
A number of factors influence the growth rate of goats. Published research on Australian goat growth rates is, however, limited and studies that report growth rates have often focused on other factors, such as cashmere production. From the limited information that does exist, it can be concluded that the average daily liveweight gain for Australian rangeland goats is generally less than 180g/day (McGregor 2005).
MLA is about to commence research to investigate rangeland goat growth rates in rangeland, mixed farming and high rainfall zones. These experiments will profile the growth rates of rangeland goats of 10 to 24kg liveweight for one year and extend current knowledge about the factors and management practices that influence growth rates.
To understand what research has previously been carried out and to help develop a plan for the current research, a literature review has been conducted. Some of the factors identified through this preliminary research will be tested in the current research to help develop a better understanding of growth rates in Australian rangeland goats.
A number of factors are known to influence the growth rate of goats:
Breed and adult size
Large goats generally have progeny with higher growth rates than the progeny of small goats. Goat breeds vary considerably in their adult size and mature weight. Small breeds, such as the Indian Barbari and Indonesian Kambing, have mature weights as low as 9 to 13kg while large breeds such as European dairy breeds and and Boer goats, can exceed 100kg. Growth rates vary from around 50g/day for small breeds to over 200g/day for large breeds (Dhanda et al. 2003). Australian rangeland goats have a mid-range mature weight of 45 to 80kg suggesting a moderate growth rate.
Birth weight and growth in early life are influenced by birth type (single, twins or triplets). Single kids have heavier birth weights and weaning weights than twins while twins have an advantage over triplets. In Queensland’s pastoral zone, single-born cashmere kids of rangeland origin were heavier at birth (average weight 2.94kg) than twins (average weight 2.5kg). At three months of age, the single-born goats remained heavier (average weight 19.0kg) than the twins (average weight 15.1kg) with the difference attributed to the heavier birth weights and higher daily weight gain of the single-born goats (141g/day) compared with the twins (105g/day) (Eady and Rose 1988).
The birth weight of kids has an effect on their growth rate until at least 12 weeks of age. In a study of rangeland and Anglo-Nubian cross goats, kids with a higher birth weight grew faster. In this study, birth weight had a greater effect on growth than did milk consumption or breed (Bajhau and Kennedy 1990). It is not clear to what degree maternal nutrition influences birth weight and growth to weaning.
Kidding history of dam
Kids of maiden does have slower growth rates in early life compared to the kids of does that have previously kidded. In a rangeland goat study, single kids of maiden does had lower average daily gain (153g/day) compared to single kids of non-maiden does (174g/day). This resulted in single kids of maiden does having an average weaning weight that was 2.1kg lighter. This early disadvantage appeared to be overcome as kids grow older, as liveweights at five months of age were comparable between the two sets of kids (Pym et al. 1982).
Sex of animal
The sex of rangeland goats has been shown to significantly affect birth weight, weaning weight and weight at five months of age. Entire males generally have higher growth rates than females. A study of Australian rangeland goats reported that males were heavier than females at birth (2.81 compared with 2.57kg), weaning (19.6 compared with 16.5kg) and at five months of age (28.6 compared with 22.9 kg) (Pym et al. 1982). Castrated male kids have growth rates that are between entire males and females; however, at the onset of sexual maturity, some studies report the growth rate advantage of intact males to be reduced or lost (for example Allan and Holst 1989).
In feeding experiments, males have been shown to grow faster than females even though feed intakes were similar. This suggests that males have a higher efficiency of feed utilisation for growth. The degree to which this advantage improves male growth rate over female growth rate appears to be dependent on feed quality, with the advantage being greater on lower quality diets. For example, on a low protein ration (10.5% crude protein), the male growth rate was 48% greater than that of females; on a high protein ration (20.5% crude protein), the growth rate of males was only 11% greater than that of females (Ash and Norton 1984).
Nutrition is the most important environmental factor influencing growth. The broad genetic base of Australian rangeland goats and associated variability in the population may make describing precise nutritional requirements difficult. The energy content of rangeland diets is the most common nutritional limitation for growing animals and has the greatest implication for growth rates. The effects will generally be more severe and long-lasting the earlier the deficiency occurs in an animal’s life.
There is strong evidence that goats, particularly bucks, have annual or seasonal growth cycles that influence their feed intake and body weight. These growth cycles are not driven by prevailing nutrition, but other factors, most likely photo-period (day length). The voluntary feed intake and body weight of bucks decreases throughout autumn and maximum growth rates occur between mid-winter and spring. In the annual cycle, buck liveweights peak in mid to late summer and are lowest during late autumn or early winter. Bucks also exhibit a seasonal reproductive cycle, where activity peaks during autumn and early winter (Walkden-Brown et al. 1994; Walkden-Brown et al. 1997).
Younger goats grow faster than older goats. In kids, a significant decrease in average daily gain has been observed as their age increases. The actual growth pattern will be heavily influenced by seasonal conditions (McGregor 2005).WeaningThe growth of kids is faster before weaning than after. In rangeland goats, there is limited information on the impact of weaning age and weaning weight on post-weaning performance. Studies of other breeds have shown a range of responses when age and weight at weaning are varied. Generally, the younger and lighter goats are when weaned, the larger the impact on performance. In some instances, the difference is not substantial and can be overcome over time.
Importance to industry
Understanding more about how various factors influence growth has potential to guide improved management practices including:
- better understanding the impact of male sexual maturity on growth rates might have important implications for management (e.g. running males and females separately) and affect marketing decisions
- determining the magnitude of seasonal changes in voluntary feed intake and growth rates, and interactions with feed quality could influence the time of marketing
- investigating how the nutrition of rangeland does in late pregnancy influences post-partum growth of their progeny. This could lead to improved recommendations for managing does in late pregnancy.
Possible management changes associated with these factors need to be considered in the context of broader production systems and in balance with other production strategies. For example:
- breeding larger goats in order to achieve faster growth rates may be difficult as larger goats may not be suited to semi-arid rangeland environments or some markets
- while single-born kids grow faster, this advantage could be offset by the larger number of goats being produced via multiple births
- greater weaning weight to achieve faster growth rate needs to be considered in relation to the impact on the nutrition of the doe at their next joining.
Trudie Atkinson and Yohannes Alemseged, NSW Department of Primary Industries, Trangie P: 02 6880 8000
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