– Michelle Arnold, DVM, Ruminant Extension Veterinarian, UKVDL
From a weather standpoint, the winter of 2016-17 has been a non-event. Record temperatures recorded in February and very little measureable snow throughout winter has been a welcome change from previous years. Despite this unexpected warmth, submissions at the UKVDL and telephone conversations with veterinarians and producers confirm many cattle are losing excessive body condition and some are dying of apparent malnutrition. This indicates winter feeding programs on many farms this year are not adequate to support cows in late pregnancy or early lactation – or their newborn calves – in spite of recent environmental conditions. If producers are not supplementing cattle with adequate energy AND protein sources, hay of unknown nutritional quality often does not provide sufficient nutrition to meet the animal’s basic requirements. This will result in depletion of body fat stores, followed by breakdown of muscle protein, and finally death due to insufficient nutrition.
Near the end of most winters, both veterinary diagnostic laboratories in KY frequently receive older beef cows for necropsy. These cows often are broken-mouthed or toothless, some are old enough to vote, are heavily pregnant or in peak milk production and in poor body condition (BCS 2-3). However, this winter, ‘malnutrition’ cases include young cows and pre-weaning/weaning age calves, indicating serious nutritional deficiencies in the feedstuffs, especially the hay produced last year. The producer may first notice a cow getting weak in the rear end then she goes down and is unable to stand. Death follows within a day or two after going down.
At necropsy, the pathologist finds no body fat stores but the rumen is full of bulky, dry forage material (hay). There is a small but definite seam of fat on the surface of the heart that is the last storage area for fat. Once this fat seam is gone, there is no fat left in the body anywhere. Despite having had access to free choice hay, these cattle have simply ‘run out of gas’ due to lack of energy and protein. Although hay may look and smell good, unless a producer has had the hay tested for nutritional content, he does not know the true feed value of that harvested forage. It is often difficult for producers to bring themselves to the realization that cattle can actually ‘starve to death’ while consuming all the hay they can eat – especially if crude protein levels are in the 3-4% range, and TDN is <40% – as is not uncommon in some late-cut overmature hay – sometimes referred to as ‘holiday hay’ or ‘CRP residue’. Inadequate crude protein in the hay (below7-8%) means there is not enough nitrogen for the rumen microflora (“bugs”) to do their job of breaking down fiber and starch for energy. Digestion slows down and cattle eat less hay because there is no room for more in the rumen. Cattle are expected to eat roughly 2.5% of their body weight in dry matter but this may fall to 1.5% on poor quality hay. Many producers have purchased “protein tubs” varying from 16-30% protein to make up for any potential deficiencies but have failed to address the severe lack of energy in the diet. Remember, in the last 60 days of gestation, an adult cow (1200 pounds eating 2% of her body weight) requires feedstuffs testing at least 54-56%TDN (energy) and 8-9% available crude protein while an adult beef cow in the first 60 days of lactation requires 59-60% TDN and 9-10.5% available crude protein.
In addition to cases of apparent malnutrition in adult cattle, there have been multiple diagnostic submissions associated with ‘weak calf syndrome’ or full-term calves which were presumed to have been stillborn. Almost without exception, there have been no gross or microscopic lesions or pathogens identified in fetal tissues or placenta, which would indicate why this happened. Maternal nutrition during the last trimester of pregnancy – particularly dietary protein levels – has been well-documented to play an important role in calf survivability. Dystocia (difficult birth) results in lack of oxygen to the calf during delivery which can result in death or weak (“dummy”) calves. Calves born to protein-deficient dams are less able to generate body heat and are slower to stand and nurse compared to calves whose dams received adequate dietary protein during the last 100 days of pregnancy. (See detailed information here: http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1151&context=rangebeefcowsymp ) Colostrum quality and quantity from protein and energy-deficient dams is not adequate for calf survival and performance. One study looking at diets during pregnancy found at weaning, 100% of the calves from the adequate energy dams were alive compared to 71% from the energy deficient dams. The major cause of death loss from birth to weaning was scours, with a death loss of 19% due to this factor.
Mineral supplementation this winter is another area of concern, as copper and selenium levels in liver samples analyzed from a large number of cases have been far below acceptable levels. Copper and selenium are vital nutrients for immune system function. Many were diagnosed with malnutrition or respiratory disease (including pneumonia in pre-weaned calves). Selenium deficiencies will lead to later reproductive problems of delayed conception, cystic ovaries and retained placentas. Additionally, grass tetany/hypomagnesemia cases received in late February in lactating beef cattle consuming only hay, with no access to fresh grass, strongly suggest 2016 hay supplies may also be lacking in magnesium.
It is important to understand that the winter of 2016-2017 has been exceptionally easy weather-wise but difficult for cattle in Kentucky. Cows of all ages are pulled down much more than typically seen in late winter. This fact, coupled with the knowledge that the quality was generally poor for hay baled in 2016, is one reason we are seeing an increase in death loss across Kentucky due to malnutrition in all ages of cattle as well as many stillborn and weak calves that do not survive. What has normally worked in years past (feeding hay exclusively throughout the winter) will not necessarily work this year.
The best advice for all producers in KY is to know your forage quality. Testing is simple, inexpensive and results are easy to interpret. If cows are losing weight, consider supplemental feed to help them through the next month to 6 weeks until grass is growing and is past the “watery” stage. Energy AND protein are both crucial; protein tubs will not be sufficient in most cases to fulfill energy requirements. Contact your nutritionist to review your feeding program. Adequate nutrition is not just important today but also down the road. Milk production, the return to estrus and rebreeding, and overall herd immunity are also impacted over the long term. Continue to offer a trace mineral mix high in magnesium in order to prevent hypomagnesemia or “grass tetany” at least through the first of May. Remember the old adage regarding the effect of winter on late gestation and early lactation cattle, “February breaks them, March takes them.” Just like a car that looks great on the outside, it will not go far without gasoline in the tank.