Dr. Travis Mulliniks, Assistant Professor in beef cattle nutrition and energy nutrition University of Tennessee, poses a very interesting question.
Read below for his incredible insight!!!! Excellent work by Dr. Mulliniks!
Beef cattle in the United States graze a variety of unique environments, which differ in climate, topography, and forage quality and quantity. These differences are accentuated by dynamic and unpredictable weather patterns and thus impact forage production and subsequently increase variability in cow performance. Animals commonly react to these variable conditions by initiating adaptive responses to cope with extreme conditions such as stress (Stott, 1981). To date, a tremendous amount of research has shown the benefit of adapted breeds of animals to certain environmental stressors. However, production practices that modify the production environment with purchased or harvested feedstuffs can buffer the coping mechanisms that livestock express. Furthermore, these production practices may start leading to less desirable and stagnant responses to environmental and physiological stresses.
Dr. Mark Petersen with the USDA-ARS Fort Keogh Livestock and Range Research Laboratory in Miles City, MT has preached that cows are athletes and should be managed accordingly. For most people, that seems like a crazy concept, but when you think about the amount of environmental pressure a cow is expected to perform under coupled with nutrient demands of lactation and reproduction, this concept becomes clearer. If athletes train to have an increased adaptive capacity and tolerance to stress, why don’t we manage cows in a similar methodology to increase their adaptive resilience to environmental stresses? However, common livestock practices tend to manipulate livestock’s nutritional environment to a degree that may completely buffer their capacity to become more adaptive and ultimately less energy efficient. In human fitness, an interesting aspect of skeletal muscle is its adaptability. If a muscle is stressed (within tolerable limits), it adapts and improves function. Conversely, if a muscle receives less stress than it’s used to, it atrophies. Therefore, adaptation requires a systematic application of environmental stress that is sufficient enough to elicit an adaptation, but not so severe that a loss in production occurs. If the stress is insufficient to overload the body, then no adaptation occurs, which is where a lot of our cow-herd management practices leads us. So can we use a model for capacity adaptability and environmental stress to increase energy efficiency and longevity of the cow herd? Is the “feed them to breed them” mentality decreasing efficiency and/or the cow’s inherent capacity to cope with environmental stress?
Adaptive capacity confers resilience to nutritional insults, given that livestock have the ability to modify their nutrient requirements with minimal losses of production. Petersen et al. (2014) illustrated that cows experiencing a dynamic environment are coping with the change by altering nutrient requirements compared with those that are in relatively static surroundings. Conversely, cows managed in the more controlled situations or static environment have a decreased aptitude for energy utilization efficiency. To illustrate this, Mulliniks et al. (2015) utilized datasets from research stations in New Mexico and Tennessee. Although, nutritional supply during the breeding season is much greater in TN, pregnancy rates were significantly less (88 vs 96% in TN and NM; respectively) in TN than in the nutrient restricted environment of NM. Input cost to achieve these production measures has to be taken into account in calculating efficiency differences. Current annual cost of production in Tennessee is $800/cow; whereas New Mexico is roughly half at $440/cow. In addition, Mayfield (2012) reports that longevity in the Tennessee herd was only 3.5 year, which is quite a bit lower than the 61% retention rate of the heifers remaining in the herd after 5 year of age (Mulliniks et al., 2013a). Thus, illustrating short- and long-term effects of adaptive capacity on cow-herd productivity.
So what happens if we take environmentally adapted heifers out of their dynamic environment and develop them in a static nutritional environment? In New Mexico, Mulliniks et al. (2013a) showed the impact of programing animals to fit their given production environment. These researchers developed yearling beef heifers on native range receiving one of two protein supplements (low-rumen undegradable protein vs high-rumen undegradable protein) or a control set of heifers developed in a feedlot. During the developmental treatment period, heifers developed in the feedlot had increased average daily gain (1.5 lb/d) from the initiation of treatments to the start of breeding compared with range-raised heifers consuming low-quality range with protein supplementation (0.58 lb/d). Even with the low average daily gain until breeding, retention rate through 5 years of age for range-developed heifers fed a high-RUP supplement was 68% compared with 41% heifers fed a lower-RUP supplement and 42% for heifers developed in a feedlot (see Figure 1 below). This study indicated the short- and long-term impact that developing heifers to fit their environment can have on biological and economic efficiency.
Figure 1. Retention rate of heifers grazing native dormant range with two types of protein supplementation (36RUP and 50RUP) or fed a growing diet in a drylot. Values shown in breeding yr 1 are heifer pregnancy rates. Breeding years 2 through 4 are proportion of the original heifers treated that were remaining at end of breeding in yr 2, 3, and 4. Retention tended (*P > 0.08) to differ among treatments in breeding yr 1 and 2, but was greater for 50RUP than 36RUP and DRYLOT cows in breeding yr 3 and 4 (**P < 0.01). 36RUP = 36% CP cottonseed meal base supplement fed 3 d/wk supplying 36% RUP; 50RUP = 36% CP supplement fed 3×/wk supplying 50% RUP; DRYLOT = corn silage diet fed in drylot to gain 0.68 kg/d. Adapted from Mulliniks et al. (2013).
Flexible and opportunistic strategies are necessary for successful management in variable environments. Successful strategies have to be engrained in a clear understanding of the challenges facing the grazing animal and its natural abilities to meet and adapt to these challenges. For example, Mulliniks et al. (2012) illustrated over a 6 year period that not all animals need to be fed to achieve a target body condition score, which allows for utilizing body storage as a nutrient source during periods of energy deficiency to maintain reproductive competence. The cows from this study were offspring of cows that were managed in a low-input ($35 to 50 per cow per year in feed inputs) production system for multiple generations. Thus, pre-planned management strategies to allow for body weight loss during periods of moderate feed restriction followed by nutrient realimentation during period of increase nutrient supply can be used to improve efficiency of energy utilization (Freetly et al., 2008).
The capacity for animals to cope with environmental changes depends on the degree of their metabolic flexibility (i.e., the phenotypic response to an environmental change). Having a high metabolic flexibility may be significantly tied to the adaptability to dynamically changing nutrient supply levels. Mulliniks et al. (2013b) illustrated the ability of livestock to modify metabolically in response to changes in nutrient availability was correlated to their timing of conception. Cows with elevated blood ketone concentrations, manifested from metabolic imbalance, prior to breeding season had a prolonged interval from calving to conception. Therefore, ketone concentrations may be a useful indicator of adaptive capacity during metabolically challenging physiological periods.
Livestock are expected to survive, grow, reproduce, and cope in dynamic and unpredictable weather patterns that create diverse environmental challenges or a combination of challenges. However, if adaptive, flexible management is not utilized, static management in the face of a dynamic problem will not yield the most favorable long-term results. With that being said, adaptive management is similar to the “bend but don’t break” philosophy. You allow a defined amount of stress to elicit an increased capacity to respond positively to the stress. With dynamic swings in environmental conditions, exploiting the natural ability of livestock to adapt in response to periods of nutrient imbalances may be an alternative strategy to manipulating the production environment. Implementing this approach may subsequently enhance adaptive capacity to environmental stresses, while increasing economic and biological efficiency.
Freetly, H. C., J. A. Nienaber, and T. Brown-Brandl. 2008. Partitioning of energy in pregnant beef cows during nutritionally induced body weight fluctuation. J. Anim. Sci. 86:3703-77.
Mayfield, W. M. 2012. Evaluating the relationship between ultrasound-derived carcass characteristics and the production traits in Angus cattle. MS thesis. University of Tennessee, Knoxville.
Mulliniks. J. T., A. G. Rius, M. A. Edwards, S. R. Edwards, J. D. Hobbs, and R. L. G. Nave. 2015. Improving efficiency of production in pasture- and range-based beef and dairy systems. J. Anim. Sci. 93:2609-2615.
Mulliniks, J. T., D. E. Hawkins, K. K. Kane, S. H. Cox, L. A. Torell, E. J. Scholljegerdes, and M. K. Petersen. 2013a. Metabolizable protein supply while grazing dormant winter forage during heifer development alters pregnancy and subsequent in-herd retention rate. J. Anim. Sci. 91:1409-1416.
Mulliniks, J. T., M. E. Kemp, R. L. Endecott, S. H. Cox, A. J. Roberts, R. C. Waterman, T. W. Geary, E. J. Scholljegerdes, and M. K. Petersen. 2013b. Does β-hydroxybutyrate concentration influence conception date in young postpartum range beef cows? J. Anim. Sci. 91:2902-2909.
Mulliniks, J. T., S. H. Cox, M. E. Kemp, R. L. Endecott, R. C. Waterman, D. M. VanLeeuwen, and M. K. Petersen. 2012. Relationship between body condition score at calving and reproductive performance in young postpartum cows grazing native range. J. Anim. Sci. 90:2811–2817.
Petersen, M. K., C. J. Mueller, J. T. Mulliniks, A. J. Roberts, T. DelCurto, and R. C. Waterman. 2014. Potential limitations of NRC in predicting energetic requirements of beef females with western U. S. grazing systems. J. Anim. Sci. 92:2800-2808.
Stott, G. H. 1981. What is animal stress and how is it measured? J. Anim. Sci. 52:150-153.