GRannie Rambouillets & Johnstone Farm Border Cheviots

Running a pasture based flock, I am trying to select for ewes that have good depth and gut capacity. These ewes can remain in good shape without massive amounts of grain in their diet.

Rambouillets and coloured girls going to fresh bale rolled out on pasture.

Many of the advantages to calving on pasture apply to sheep lambing in pasture

Sheep are truly fascinating from a resource utilization standpoint, especially when you consider that the most challenging production time points of breeding an...d the critical early stages of pregnancy occur during a time of the year when our forage resources are at their lowest nutritive value, and temperatures are the least favorable. Yet, even with their resilience to the cold weather we need to be aware of the added risks during inclement weather season and have a strategic response on our operation. Thermal Balance Sheep maintain a relatively constant core temperature by balancing the heat gained from metabolism against that gained from or given up to the environment. The thermal environment has a strong influence on farm animals with air temperature having the primary effect, but altered by wind, precipitation, humidity, and radiation. Under most conditions there is a continual net loss of sensible heat from the body surface through conduction, convection, and radiation. Under all conditions there is a continual loss of insensible (evaporative) heat from the respiratory tract and skin surface. Thermoneutral Range Sheep The thermoneutral range for mature ewes is 24 to 66 F. This range, also known as effective ambient temperature, is the most comfortable range for the sheep (thermal-comfort zone). Their metabolic heat production is constant in this temperature range and this environment promotes maximum performance with the least stress (heat or cold). Within the thermo-nuetral zone there is a cool zone where behavioral changes take place to conserve body heat i.e., vasoconstriction of peripheral blood vessels, adjustments in posture, and grouping together. Visual observation of some of these changes can help producers identify when animals are approaching cold thresholds. Yet, even with the sheep’s behavioral ability to alleviate lowering temperatures, once the lower critical temperature threshold is surpassed the animal must produce metabolic heat from dietary sources. Lower Critical Temperature can be a misnomer as it refers to the ideal temperature for the animal, not the coldest temperatures it can handle. This only implies the lower range of the optimum temperature range where the sheep will need to rely on heat generated from metabolic activities (cellular respiration, absorption, and heat of fermentation in rumen). One reason sheep are so resistant to cold stress is the super insulative value of their fleece, yet even this is dependent on staple length. For example, inch staple length is a threshold where insulative properties of the fleece are greatly diminished. Wind Chill By means of a wind-chill index, the combined effect of ambient temperature and air speed on environmental heat demand is represented by a single value. Wind-chill indices have been developed for various species in cool and cold environments. During high wind velocities (> 25 mph) the wool fibers are separated which decreases the insulative properties of the fleece and accelerates heat loss (Ames and Insley, 1975). Precipitation A combination of low temperature, wind, and rain or wet snow can adversely affect an animal's heat balance. Rain causes heat loss through evaporative heat loss and thermal conductivity by falling on the skin. Water accumulates in an animal's wool, displacing still air, thereby reducing external insulation. In addition, freezing rain and ice may flatten the wool, thereby reducing its depth and thus insulative value. Snow or cold rain increases conductive heat loss, then drying of the wool cools the animal through evaporative heat loss. Matted fleeces due to mud or manure also decrease the sheep’s ability to thermo regulate. Shearing and Intake Requirements Intake increases after shearing are generally a result of the increased heat production required to maintain body temperature. Research has shown that shearing pregnant ewes has been shown to increase lamb birth weight without negatively impacting ewe body condition and body weight at lambing (Keady and Hanrahan, 2009). In growing lambs, a 10% increase in lamb dry matter intake (2.84 vs 3.06 lbs) was observed by Keady and Hanrahan (2015). Calculations from Brink (1975) found a linear increase in dry matter intake from 24 to 90 F. From these calculations 88 lb freshly shorn lamb would consume 4 lbs of feed at 24 F yet only consume 3.3 lbs at 90 F. Whether you hand feed or use a bale proccesor, a simple rule of feeding 15 to 25% in the weeks post-shearing is a sound-policy. Feeding Recommendations Voluntary intake increases when temperatures fall below the thermoneutral threshold of 24 F. Christopherson (1976) observed decreased digestibility at lower temperatures. For example, a low quality grass hay might have a 54% digestibility at 68 F but only a 47% digestibility at 23 F. Thus, under periods of prolonged cold, it’s advisable to not only provide more feed but feed of a higher quality (second cutting hay vs. first cutting hay), or added supplemental protein that might aid in fiber digestion if low-quality hay is the majority of the basal diet. Fiber has a high heat increment when compared with concentrates (Baldwin et al., 1980). The greater heat increments fed during cold periods creates a sparing effect on net energy for production (i.e., fetal growth, average daily gain, milk production). For pregnant ewes, the decreased rumen volume due to fetal growth (especially multiple carrying ewes) limits digestive capacity and restricts increased intake. If available supplementation with highly fermentable fiber (e.g., soyhulls, wheat middlings) and energy dense concentrates (e.g., corn, oats, barley, peas) can alleviate metabolic demands for both the ewe and unborn lamb especially during inclement weather. However, it’s important to gradually adapt ewes to these energy dense sources and generally should not exceed 1.5 lb. per head per day, as a rule of thumb. Timing and Planning In the digital age it is much easier to anticipate an oncoming storm. The digestive process in ruminants such as sheep can extend 24 to 48 hr after feed is consumed, and thus providing extra feed 12 to 24 hr in advance gives the upper hand and allows heat energy produced from the feed to kick in prior to the cold stress. The slow process of digging out snow or fighting mud further delays getting feed in front of the sheep and can put undue stress on ewes, especially during late gestation. Feeding 25% to 50% more a day or two in advance of the storm will pay dividends during a prolonged cold snap. The idea of a rainy day hay or feed supply is a sound strategy when preparing for inclement weather. References Due to space requirements references are available upon request of the author [email protected]