Animal Production, Average Daily Gains and Body Temperatures 

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Chapter 3: Animal Production, Average Daily Gains and Body Temperatures

Introduction

Livestock producers must balance their desire to farm, economics, environmental impact, and animal productivity to maintain farm vitality and success. A USDA survey of cattle producers identified animal welfare as a top need for research needs (#3) among cow health (#1), calf health (#2), nutrition (#4), and biosecurity (#5) (USDA, 2016). Producers have the desire to improve animal welfare on their operations. Current research indicates that animal welfare and animal comfort are related to animal productivity (Silanikove, 2000; USDA, 2016; Polsky and von Keyserlingk, 2017). Furthermore, consumers are more interested in animal welfare as consumers want to be more involved in their food making decisions and knowledgeable about where their food comes from (Henderson, 2018). Animal production and animal welfare both play a role in producing healthy, profitable, and desirable animal and food products.
Animal production is a complex process involving the specific animal and its requirements, feed consumption, environment, health, and genetics. Basic animal science teaches that an animal’s phenotype or outward performance is the combination of genetics plus environment. The environment is not only measured by the physical surroundings but is also impacted by stress management and welfare (National Research Council, 1996). Animals partition energy (input and output) towards different needs to meet their requirements. The four main categories of animal energy expenditure are maintenance, lactation, growth, and reproduction. Maintenance is an animal’s first priority in determining energy requirements before spending energy on growth, lactation, and reproduction; if an animal is nursing offspring, then nutrients may be diverted for lactation as a higher priority (National Research Council, 1996).
When animals are under heat stress, one typical response is to decrease feed intake, which limits nutrients available for energy expenditure (Blackshaw and Blackshaw, 1994; National Research Council (U.S.), 1996). Two major measures of heat stress are external and internal body temperature (Scharf et al., 2011). External hide temperature is directly related to the heat load an animal is exposed to as a result of their environment. Meanwhile, internal body temperature is a function of an animal’s ability to maintain body temperature in response to heat stress (Collier et al., 2017). Increases in body temperature, both internal and external, identify heat stress on the animal. Natural behaviors and animal processes are expected to cause some fluctuations in internal temperature; specifically, digestion and metabolism produce heat which impacts an animal’s heat load (Blackshaw and Blackshaw, 1994). If an animal is not capable of handling this heat load, they will, in response, decrease feed intake. As a result, when an animal is not consuming enough energy through feed, whether by a lack of availability or by decreased consumption in response to environmental stress, those secondary processes requiring energy (growth, lactation, reproduction) are inhibited. Stress, whether brought out by heat, handling, or disease, may additionally aggravate animal production, welfare, and health (Blackshaw and Blackshaw, 1994; Nienaber et al., 1999).
Liveweight gain is a primary benchmark of production in the beef cattle industry since animals are sold based on body weight. Any business or production change, and therefore any research claim, in the beef cattle industry must ensure that recommendations are complementary to production and thus, economically feasible. In a silvopasture system, animal liveweight gains are only part of the total equation. Even lower gains in silvopastures than in open pastures may still result in more productive systems. Silvopastures also produce economically valuable trees for timber, among other environmental and aesthetic services. A land equivalency ratio may be used to compare the productivity of an integrated system, like silvopasture, versus the production of commodities raised or grown separately (Mead and Wiley, 1980; Sharrow et al., 2009).
In a silvopasture, the LER would be calculated by the production of the animals in a silvopasture as compared to an open pasture, plus the production of trees in a silvopasture over typical forest production. If this ratio is greater than one, the integrated system is more productive than when the production of trees and livestock are managed separately.
The presence of shade has often resulted in increased production of animals (Blackshaw and Blackshaw, 1994; Silanikove, 2000; Veissier et al., 2017). However, other studies specifically within silvopastures, have seen no change or minimum differences in ADG among animals in silvopasture systems compared to animals in open systems (Kallenbach et al., 2006; Costa et al., 2016; Pent, 2017). As such, the stocking rate was not adjusted in accordance with the reduced forage availability. Heat stress negatively impacts animal reproductive success, including reproductive system development and conception and pregnancy rates (Shearer et al., 1999), and decreased lactation. Livestock under heat stress exhibit increased panting, respiration rate, and internal temperature, but these physiological and behavioral responses may be ameliorated through the provision of shade (Silanikove, 2000; Rovira, 2014; Allen et al., 2015; Ammer et al., 2016; Veissier et al., 2017).
The objectives of this study were to:

1. Evaluate change in liveweight gain among heifers in open pastures and silvopastures throughout the summer.
2. Identify fluctuations in internal vaginal temperature in heifers without access to shade and heifers with access to either shade from pine trees or hardwood trees.
3. Compare changes in external hide temperatures of heifers in the morning and afternoon with and without access to shade.

Materials and Methods

Site Description

This work was performed at the Southern Piedmont Agricultural Research and Extension Center (SPAREC) in Blackstone, Virginia (37.091889, -77.963632). This protocol was approved by the Virginia Tech Institutional Animal Care and Use Committee (Protocol #17-071). Soil series at the site location consisted primarily of a Durham coarse sandy loam, undulating (Fine-loamy, siliceous, semiactive, thermic Typic Hapludults) with smaller areas consisting of Worsham sandy loam (fine, mixed, active, thermic Typic Endoaquults) and Appling coarse sandy loam (fine, kaolinitic, thermic Typic Kanhapludults; Soil Survey Staff, 2018). An onsite WatchDog 2000 series 2900 ET weather station (Spectrum Technologies, Aurora, IL) collected weather data at SPAREC at 15-minute intervals. The average temperature and rainfall for the study and the 30-year average are listed in Table 3.1.
An existing timber stand was thinned or clear-cut to establish silvopasture and open pasture treatments beginning in 2014-2015. Treatment pastures (2 ha/experimental unit) were replicated twice and consisted of open pasture, newly planted pine silvopasture, thinned pine silvopasture, and thinned hardwood silvopasture. The open pastures and newly planted pine silvopastures were completely cleared of trees. The newly planted pine silvopasture was then replanted with loblolly pine seedlings at 2.4 m spacing between seedlings in triple row sets with varying alley widths between tree rows (6, 12, and 18 m). The two types of thinned silvopastures were thinned to 30% of the basal area of the previous tree density equating to 10.6 m² ha^-1 and 8.7 m² ha^-1 in the thinned pine and hardwood silvopastures, respectively. The presence of hardwood or pine trees was based on trees present in the original stand. All pastures were disked, mulched, and fertilized as recommended by the soil test and planted with a cool-season mixture of novel tall fescue (Schedonorus arundinaceus (Schreb.) Dumont., syn. Lolium arundinaceum (Schreb.) Darbysh., formerly Festuca arundinacea Schreb.) infected with a novel endophyte (Neotyphodium coenophialum ‘E34’), meadow fescue (Schedonorus pratensis (Huds.) Beauv.), orchardgrass (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.), red clover (Trifolium pretense L.), ladino clover (Trifolium repens L.), and alfalfa (Medicago sativa L.). Half of the pastures were planted in the spring of 2016 along with a pearl millet (Pennisetum glaugum (L.) R. Br.) nurse crop, and the other half of the pastures were planted in the fall of 2016 without a nurse crop.

Animal Stocking

Prior to each summer season, forty fall-born heifers were brought to the Southern Piedmont AREC in May after being weaned in Blacksburg, Virginia. The animals were acclimated to the new farm for a few weeks each summer in a single herd. Following this period, treatment pastures were prepared for animal introduction by setting up temporary electrified tape in each pasture. Animals were weighed once daily on two consecutive days. After the initial weighing, animals were stratified according to their initial weights and then randomly assigned to one of eight groups at a rate of 5 heifers per 2 hectares, placing similar kilograms of animal per hectare on each treatment pasture. After the second day of weighing, animals were divided into their respective groups and moved to their respective pastures. Mean heifer weights of the start of the study were 279 kg and 268 kg in 2017 and 2018, respectively. Heifers were rotationally stocked throughout the summer in accordance with forage availability with the goal of leaving a 5-8 cm residual sward height. In 2017, heifers were stocked on pasture treatments in June, July, and October; heifers were removed at the beginning of August due to lack of forage availability in treatment pastures following the summer dry spell and were put back on treatment in October after forage regrowth. Pastures had not been grazed prior to June 2017. Heifers were stocked May-August in 2018 but were returned to Blacksburg for breeding prior to October grazing. Cattle were rotated every 1-2 weeks based on forage availability. Following heifer removal at the end of the study each year, all pastures were clipped with a rotary mower to a uniform height between 10-15 cm and again clipped the following spring of 2018 at 10-15 cm to keep forage in a vegetative state.

Animal Daily Gain

Prior to animals being introduced to treatment pastures, animals were weighed once daily for two days to obtain an initial weight and placed out on treatments. Heifers were weighed every 28 days. Weight changes were divided by the duration between weigh dates to determine average daily gain.
In 2017, animals were on treatment between June 19, 2017, and August 4, 2017, and again between September 6, 2017, and October 26, 2017. Heifers were removed from treatments at the end of the summer period on day 56, as a result of inadequate forage. Animals were then grouped together in a nearby open pasture until the forage had regrown to sufficient levels. Heifers were weighed prior to reintroduction on day 91 and 92. Animals were rotated in treatment pastures until day 140, for a total of 51 days on treatment in fall. In 2018, heifers were on treatment between June 19, 2018, and August 13, 2019.

Evaluating Cattle Internal Temperatures with Blank CIDRs

A blank controlled internal drug release (CIDR) device was hollowed out using a utility knife to fit a cylindrical Star-Oddi DST micro-T temperature logger (Star Oddi, Iceland). Mercury 4.91- DST micro-T software was used to synch Star-Oddi temperature loggers, and loggers were placed in the blank CIDRs (Fig 3.1). The devices were secured with electrical tape similar to Burdick et al. (2012). The CIDR and temperature probe were inserted with an Eazi-Breed CIDR applicator for cattle and lube using standard CIDR implant protocol (45 degrees in, straightening, cleaning). CIDRs were inserted into two heifers from each group with the exception of animals in the newly planted pine silvopasture treatments. Animals were returned to treatment pastures for the collection period. Vaginal temperatures were recorded every 10 minutes for a period of 4 days before the device was removed from the heifers. Temperature probe data was downloaded with the software and then analyzed for temperature changes throughout the day between groups. CIDR implant insertion occurred on July 17 and August 9, 2018. CIDR implants were removed on July 20 and August 13, 2018.

Chapter 1: Literature Review 
Introduction
Literature Review
Cattle Heat Stress
Silvopasture Production
Conclusion
References
Chapter 2: Forage Production and Nutritive Value in Silvopastoral Systems 
Introduction
Materials and Methods
Site Description
Animal Stocking
Forage Availability
Forage Nutritive Value
Statistical Analysis
Results and Discussion
Forage Availability
Forage Nutritive Value
Chapter 3: Animal Production, Average Daily Gains and Body Temperatures 
Introduction
Materials and Methods
Site Description
Animal Stocking
Animal Daily Gain
Evaluating Cattle Internal Temperatures with Blank CIDRs
Statistical Analysis
Results and Discussion
References
Chapter 4: Growing a Silvopasture 
Introduction
Materials and Methods
Site Description
Animal Stocking
Tree Score Evaluation
Statistical Analysis
Results and Discussion
Tree Score Evaluation
References
Appendix
Chapter 5: Conclusions 
Conclusions and Future Research
Forage Availability and Nutritive Value
Livestock Production in Silvopastures
Growing a Silvopasture
Conclusion
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Linking Cattle, Forage and Tree Production in Silvopasture Systems