Monday, August 17, 2015

Life support - Goats

Another entry in the series of animal yields and requirements.

Let's consider a herd of 100 producing goats, just as we did for dairy cattle. The required protein in feed is 16% (with short periods at 20%); as ruminants these animals require plenty of bulk fiber. (It is possible to raise goats without roughage, basically forcing them not to develop their rumen; this is protein-intensive and cannot be used for herd replacement.)

 The lactation cycle for goats ranges from 275 to 305 days, averaging 290 days productive and 75 days dry. That means there are 26 dry goats in the herd. Males should be provided at a rate of about 1:25, so 5 adult males are required. The young are fertile within 7 months of birth or 12 months of conception, so there are no juveniles over 1 year old aging into production. Culling rate is about 16%, so each year will see 20 does harvested and about an 80% chance of taking one of the bucks (assuming 21 total per year). The birth rate for goats is about 2.2, with twins being the most common and with triplets outnumbering singles. Survival rates for triplets are fairly low. The herd produces 277 kids, of which about 10% will not survive through weaning. The remaining 250 kids should be about even between sexes. The single best male will be raised to replace breeding stock and the top 20 females will be raised as replacement does. The remaining 229 will be raised for meat, to be slaughtered at 6.5 months from birth.

 Each lactation produces between 825 and 1170 kg of milk; this is strongly dependent on breed. Higher producers tend to have lower fat and protein content, so on a fat-content basis their output is about the same. Yields as high as 2490 kg per lactation have been reported for Saanen or Alpine does. We will assume Alpines or similar at 1030 kg per lactation, so the herd produces 103 tons of milk each year. Feed efficiency is pretty close to 1 for producing does only, or 103 tons of feed for the year. (See also "Dairy goats feeding and nutrition" pp.150)  Nonproducing animals consume about 3% of body weight per day at 60kg for a total of about 20 tons of feed per year. That gives a whole-herd FCR of about 1.2 for milk production.

 Kids are weaned at around 8 weeks, with an FCR at 16 weeks of about 3 and a weight of 19kg. Further growth to 24.5kg occurs with an FCR of about 3, then to 36.5kg with an FCR of about 6 (table 2) at 6.5 months of age. This would require 36.4 tons of feed, yielding an overall FCR of 4. Continued growth would see an FCR of about 8 through the 12th month with average daily gain around 150 grams, or a final weight of 61kg for an additional 49 tons of feed and an overall FCR of 5.6. Since our objective is efficient production, I assume animals will be harvested at maturity (6.5 months). The 21 adults culled annually mass 60kg and yield 27% boneless meat {see figure 2} (341.6kg), while the 229 harvested juveniles mass 36.5kg and yield the same 27% boneless meat (2,256.8kg). This will require 36.4 tons of feed plus an extra 4.1 tons for the 21 replacement animals, a total of 40.5 tons and a live-weight FCR of 4.21.

 Space requirements are about 1m² per doe, 0.33m² per kid and 2.5m² per breeding male. This flock requires 221m²; the entire area needs to be human-accessible or about 2m high, so the volume required is 442m³. Production of milk is 1.277 kg/m²*day. Production of meat is 32.2 g/m²*day.

 On a per-kg waste basis this is 14 grams meat + 562 grams milk. Compare that to dairy cattle's 16 g beef + 1.094 kg cow's milk and it seems goats are not actually more efficient that cattle. Admittedly, the goat's milk is much richer than the cow's milk. Also, it is not possible to make the cattle herd much smaller; the goat herd could be one-fifth this size and still be viable. For habitats that are sharply constrained by available space, goats may be a viable option when cattle are not.

This analysis ignored meat breeds and meat hybrids; if a suitable high-producing dairy and meat cross could be identified then the numbers might be improved somewhat. Boer crosses for example might reduce the FCR by up to 1 point and increase the live mass by up to 30kg during the juvenile growth stages, potentially leading to larger and more efficient meat yields without reducing dairy yields. I have also ignored fiber production mainly because the best fiber producers are slow growers with poor milk yield.

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