Angora Cold Mortality and the Shearing Decision

#The goat that cannot hold its blood sugar

An Angora that dies in a cold front does not simply freeze. It runs out of glucose.

Two decades of Grootfontein research resolve into that one mechanism. The practically important abortion type in Angoras is stress- and nutrition-induced: a drop in maternal blood glucose produces the same hypoglycaemia in the foetal circulation, which activates the foetal hypothalamic-pituitary-adrenal axis, driving an oestrogen surge, luteolysis and delivery (Wentzel, GADI). The same abrupt glucose collapse accompanies the death of a cold-stressed Angora — confirmed by how fast a collapsed animal recovers when a veterinarian gives it isotonic glucose in a clinical setting.

So the abortion problem and the cold-death problem are not two problems. They are one problem with two outcomes, and both are energy problems. You do not manage Angora cold loss with shelter alone, and you do not manage it with feed alone. You manage it by never letting a predictable stress arrive on top of an empty energy tank.

One honest note on the mechanism. You will hear the Angora described as having an abnormally low cortisol output. That claim is not in the Grootfontein review it is usually attributed to, and no primary source for it could be found. What is documented is the glucose collapse. Teach the glucose, not the cortisol.

#What it used to cost, and what fixing the energy did

The historic numbers show how large a manageable problem can get before anyone measures it. Surveys recorded losses of up to 80% of the potential kid crop on some farms, with kidding rates under 60% generally accepted as normal in the industry (Wentzel, citing Van Heerden 1963).

Then Grootfontein worked out that the constraint was energy, and the industry adopted energy supplementation around the predictable stresses. Reproduction rose to roughly 80%, and average mohair production climbed from 3.18 kg in 1960 to more than 4 kg per animal. Flushing trials with treated grain raised kidding rates from 17% to 60% in the worst cases (Wentzel).

That change came from understanding a metabolism, not from a new breed.

Note what is not unusual about the Angora. Its maintenance and growth energy requirements do not differ significantly from other goats' — maintenance around 434.9 kJ ME per kg metabolic weight per day, against published values of 424.3 and 432.8 for goats generally. The outlier is hair: about 136.8 kJ ME per gram of fibre, roughly three times the NRC value of 45.8 (Herselman & Smith). The Angora is an ordinary goat carrying an expensive fibre habit. That is why its energy margin is thin, and why a cold front finds it first.

#The scale of the modern problem

Cold shows up in the kid crop too, though less than most farmers assume. Across 12 Angora studs and 17 534 kids between 2000 and 2004, pre-weaning mortality averaged 11.5%, ranging from 3.0% to 17.1% between studs. Where a cause was identified, predators accounted for 39.1% of deaths and rain and cold for about 5.3% — but the cause was unknown for 70.2% of all deaths (Snyman). Treat that 5.3% as a floor, not a measurement.

#Rowswell's two rules, and why only one of them is the answer

In 1985 Rowswell took 122 farmer-reported goat death dates going back to 1970 from the twenty highest mohair-producing districts and matched them against records from 26 weather stations. The purpose was practical: to tell a farmer when it is safe to shear (Rowswell, Karoo Agric Vol 3 No 5, 1985).

He built two criteria sets, and they are constantly conflated. They are not a range. They are two tests with two different answers.

The second is the one Rowswell recommends, and the reasoning is the most instructive part of the study. A 10 °C minimum can occur on a summer morning that reaches 30 °C by afternoon. That is a thunderstorm, not a killer. A 10 °C mean daily temperature forces the whole day to stay cold — the slow, frontal, wet, overcast pattern that strips an animal's energy over hours. The criterion has to select frontal weather, not convective weather, and the mean does that while the minimum does not.

Two features of the resulting maps convert directly into management. January and February recorded no qualifying days at any station — high-summer risk is effectively zero across the belt. And high-probability isolines encroach on large areas in July and August, the peak. On the annual three-criterion map, the north-east around Middelburg, eastern Cradock, Somerset East, Bedford, Adelaide and Cathcart, the southern central area around Uniondale, Steytlerville, Uitenhage and southern Willowmore, and the extreme south — where the annual figure reaches 100% — sit above average.

#Building the tool: your station, your window

Get ten years of daily records for the station nearest you — rainfall, maximum and minimum temperature. Compute the daily mean as (maximum + minimum) ÷ 2. Flag every day where rainfall ≥5 mm and mean daily temperature ≤10 °C. Count the flagged days per calendar month across the ten years and divide by the days in that month across the ten years. That is your own monthly danger-day probability, in Rowswell's currency.

Say your station comes back like this: January and February 0%, March 2%, April 6%, May 14%, June 22%, July 27%, August 24%, September 15%, October 8%, November 3%, December 1%.

Now price a shearing date. The documented high-risk window is the first few weeks after shearing — call it 21 days. The expected number of danger days inside that window is simply the monthly probability multiplied by 21.

• Shear on 1 July: 0.27 × 21 = 5.7 expected danger days in the vulnerable window.
• Shear on 1 October: 0.08 × 21 = 1.7 expected danger days.
• Shear on 1 February: 0.00 × 21 = zero.

That is why the summer shearing is the easy one and the winter shearing is the one that needs a plan. It does not tell you to shear only in February — the fibre and the selling seasons will not allow it. It tells you how much shelter, coat capacity and supplementary energy the winter shearing has to buy, and it gives you a number to put in front of a shearing contractor when you ask to move a date by three weeks.

#Do coats pay?

Grootfontein exposed shorn castrated Angora kids to the equivalent of 5 mm of rain every 60 minutes for five hours — 25 mm in total — in a shaded area exposed to wind, in two runs of 24 and then 30 animals.

At 300 minutes the coated animals were 1.91 °C warmer rectally — 36.49 °C against 34.58 °C — and had dropped 2.21 °C less on average. Six control animals fell below 34 °C, against one coated animal (protective coats trial).

Read that as a farmer. Coats did not abolish the drop; they slowed it. One coated animal still went below 34 °C. The single collapse below 32 °C was a control animal, revived in a heated room by a clinical procedure — which is the practical point: a collapsing Angora is a call-the-vet event, not a needle-and-guess event.

So coats are a real, measured, partial intervention. They buy hours in the window where hours decide the outcome. They do not replace shelter, and Grootfontein records that kraaling in sheds — still the most common preventive measure — has become less viable as enterprises got more extensive and labour law changed. Agribook's corollary from the industry side is that shelter and post-shearing supplementary feeding are both required, and that shelters usually have to be built in more than one place on an extensive farm. That is a capital line, not a good intention.

Pull ten years of daily rain and temperature for your nearest station this week and build the monthly table. If it tells you your winter shearing sits in a 25%-danger-day month, you are not choosing between shearing and not shearing — you are choosing between building the shelter now and paying for the animals later.