Synopsis

Global analyses have clearly shown that non-CO2 greenhouse gas (GHG) emissions [(i.e., enteric methane (CH4) and nitrous oxide (N2O)] are inversely related to animal productivity (Gerber et al., 2011). Higher producing animals consume more feed, produce more manure, and emit more significant absolute amounts of GHG from enteric fermentation or during manure storage and application or deposition than low-producing animals. Converted per unit of animal product; however, higher-producing animals usually have lower GHG emissions than low-producing animals. Therefore, enhancing animal productivity is usually a successful strategy for mitigating GHG emissions from livestock production systems. Discussions presented in the current analysis are based primarily on a recent review of mitigation measures for livestock by Hristov et al. (2013b). The present paper is the third of 3 reports focusing on analyzing published data on GHG mitigation options related to animal management, including improving animal genetics, fertility, and animal health and longevity. The first (Hristov et al., 2013a) and second (Montes et al., 2013) papers in this series address enteric CH4 emissions and CH4 and N2O emissions from manure decomposition, respectively. Gerber et al. (2013) discussed interactions among mitigation practices.

Commentary

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Analysis

ANIMAL FERTILITY

Data from the literature on animal fertility are summarized 2. Poor fertility increases GHG emissions from animal production systems (Dyer et al., 2010; O’Brien et al., 2010; Crosson et al., 2011); primarily, poor fertility causes livestock producers to maintain more animals per unit of production and keep more replacement animals to maintain herd or flock size (Garnsworthy, 2004; Berglund, 2008; Wall et al., 2010; Bell et al., 2011). Garnsworthy (2004) concluded that improvements in infertility could reduce CH4 emissions by 24% and NH3 emissions by 17%, primarily by reducing the number of replacements in the herd. In the global dairy industry, there has been a general decline in fertility that is indirectly associated with aggressive selection for production traits. Roughly one-third of the reduction in fertility in dairy cattle over the last 40 yr is estimated to be related to genetic selection for production and increases in inbreeding (Shook, 2006; Huang et al., 2010).

However, this trend has recently been slowed and even reversed in developed countries due to the greater emphasis on fitness and fertility traits in selection indexes and acceptable management practices to counteract these declines (Funk, 2006). Nutritional status, the timing of the initial insemination after parturition, and the method and timing of pregnancy diagnosis of females are key factors that interact to determine fertility (Mourits et al., 2000). In many parts of the world, especially developing countries, inadequate nutrition is the primary factor limiting fertility. However, even in these areas, there are low input approaches that can be, and in some cases, are being implemented to increase fertility. Examples of low input approaches to increase fertility include reducing inbreeding (Zi, 2003; Berman, 2011), sire mate selection from highly fertile animals, reducing stressors, and improving education on the factors influencing fertility (Banda et al., 2011).

Use of reproductive technologies where they are available and cost-effective, such as genetic and genomic selection for fertility (Tiezzi et al., 2011; Amann and DeJarnette, 2012), AI (Lopez-Gatius, 2012). Gender selected semen (i.e., sexed semen; Rath and Johnson, 2008; DeJarnette et al., 2011), embryo transfer (Hansen and Block, 2004; Longergan, 2007), and estrous or ovulation synchronization (Gumen et al., 2011) increases reproductive efficiency and reduces the number of animals and GHG Ei (Garnsworthy, 2004; Bell et al., 2011). In particular, failure to use AI and cost-effective results in increased numbers of animals per farm (males) and reduced genetic merit for production and reproduction traits. In this regard, there is growing evidence that governments of developing countries can effectively lead efforts to facilitate the use of AI and significantly accelerate genetic progress, provided these efforts include all stakeholders, are comprehensive, and include improvements to facilities and markets (FAO, 2011b).

Choice of Breed and Mating Strategies

Indigenous breeds reflect generations of selection to survive in environment-specific conditions and with local feed resources and management. Often equally crucial to smallholder farmers are appearance traits that may or may not be related to productivity; examples include coat color, tail type, and presence and type of horns (Duguma et al., 2010; Gizaw et al., 2011). Selection for survival (e.g., heat tolerance, parasite resistance) and appearance traits has, in many cases, come at the expense of fertility and production traits (Berman, 2011). In addition, there are numerous examples of introductions of nonadapted breeds into regions to realize rapid gains in production (Berman, 2011). However, these often fail or fall short of expectations because the introduced breed cannot thrive under local conditions or fails to deliver acceptable appearance traits. Therefore, breeds of animals in production systems should be selected based on their superior performance in the local and regional environment and with consideration to local preferences and infrastructure, personnel (management skills), and feed resources.

The trend in recent years has been to take a crossbreeding approach using nonadapted breeds crossed with indigenous breeds (Berman, 2011; Banda et al., 2011) or to use indigenous breeds in the context of a nucleus flock or village-based selection program to accelerate genetic progress. Although this can result in slower gains in production efficiency, it is more effective in ensuring that crossbred animals have the needed survival traits (Funk, 2006; Bee et al., 2006) and that animals possess culturally appropriate appearance traits. For example, Mirkena et al. (2012) described an approach where numerous small flocks in a village were treated as one large population, and selection for breeding males was made from that larger group. In other cases, governments, non-government organizations, or academic institutions can establish nucleus flocks to distribute high-quality genetics. Using these approaches yielded significant gains in both lambs born and weaned per ewe (Mirkena et al., 2012). Still, the authors concluded the method relied on accurate pedigree and performance information and a commitment of continuing support for the program.

In many countries, including many developed countries, pure-breeding is used extensively for genetic improvement. It provides founder animals for effective crossbreeding programs if careful attention is paid to breeding strategies to minimize inbreeding and incorporate fertility measures into selection indices. During the past decade, selection indexes for Holsteins in the United States have increased emphasis on fertility measures (daughter pregnancy rate and productive life) with evidence of success (Kuhn et al., 2006; VanRaden et al., 2007; Norman et al., 2009). Regions that have consistently included fertility in selection indexes have not seen the same declines in fertility while achieving substantial gains in production (Berglund, 2008). Whereas this can be accomplished in developed countries, it is more difficult in developing countries where availability of breeding animals of the introduced breed may be limited, pedigree information is incomplete or absent, and the cost of genetic analysis is often prohibitive.

Increasing emphasis on fertility and productive life in selection indexes will reduce animal numbers needed to produce a unit of product. Inbreeding-induced reduction in fertility is also an issue associated with pure-breeding. The widespread use of North American dairy genetics has resulted in a global increase in inbreeding coefficients among major breeds (Funk, 2006). Whereas pedigree driven mate selection is a common practice to reduce inbreeding in developed countries, this is not the case for many developing countries. For example, in sheep production in Ethiopia, approximately 75% of farmers replaced their breeding ram from their own flock (Getachew et al., 2011). Similar observations have been made in Bhutan, Nepal, India, and China, where smallholder Yak farmers select replacement males from their own sires and use the same male even as his own daughters reach breeding age (Zi, 2003). Education and temporary mixing of flocks or herds are low input strategies to reduce the adverse effects of inbreeding on fertility and should be strongly encouraged.

Early Puberty Attainment and Seasonality

Reproductive efficiency can be improved if animals are managed to achieve puberty early, which can be accomplished through genetic selection (Nogueira, 2004; Fortes et al., 2011), improved metabolic status (Funston et al., 2012), and manipulation of the season of birth (Luna-Nevarez et al., 2010; Fortes et al., 2011). The result of these strategies is to allow for insemination and first parturition to occur at a younger age. For example, under conditions of adequate nutrition, swine should be inseminated on their pubertal estrus to maximize lifetime productivity (Kirkwood and Thacker, 1992). This results in an early economic return on investment and enhanced profitability, a more rapid introduction of improved genetics into herd or flocks, and more pregnancies during the animals’ productive life (Place and Mitloehner, 2010). Primary factors limiting this approach are the ability to meet the nutritional needs of growth and gestation during the first parity and management skills of farm personnel.

Reduction in (or alteration of) seasonality provides opportunities to produce offspring for the market when prices are highest. In addition, for sheep and goats, it opens up the possibility of obtaining two lambings or kiddings in 1 yr, effectively doubling production per female (Notter, 2008). However, these accelerated lambing systems require intensive management, adequate facilities, early weaning, and optimal nutrition. The effects of season on fertility have also been demonstrated in cattle (De Rensis and Scaramuzzi, 2003), buffalo (Perera, 2011), and swine (Kirkwood and Aherne, 1985). Strategies to address seasonality in these species (especially buffalo and cattle) include increasing metabolic status and reducing heat stress by the provision of adequate shade and access to water.

Enhanced Fecundity

Prolific breeds or strains of animals can significantly increase the efficiency of production by increasing the number of animals (or BW) weaned per female for each gestation. However, breed choice must meet the requirements for appearance traits, adaptation to regional climate, feed, and production and management practices (Getachew et al., 2011). This approach is relevant for small ruminants and less relevant to cattle production because twins are generally not favored due to the resulting increase in periparturient problems (dystocia, uterine infection, or delayed resumption of cyclicity). Several sheep breeds (e.g., Finnsheep, Romanov, Boorola Merino, etc.) exhibit increased ovulation rate and litter sizes. In addition, standard gene introgression (mating) strategies have been used to improve fecundity in existing breeds without losing desired breed characteristics and appearance traits (Notter, 2008).

For example, the unimproved version of the widely used Awassi and Assaf breeds (fat tail sheep) in the Middle East have been introgressed with the Boorola Merino fecundity gene (FecB gene) resulting in the Afec Awassi and Afec Assaf breeds that exhibit a yearly increase of approximately one additional lamb per ewe (Gootwine, 2011). A similar approach using the fecund Indian Garole breed crossed with the Laland strain of the Deccani breed on the Deccani plateau in India resulted in a 33% increase in productivity of ewes carrying the FecB gene (FAO, 2011a). However, the success of this program was dependent on additional support for the smallholder farmers, including training in lamb management, veterinary care, and insurance payments. The FecB gene mutation is also present in several other Asian breeds including the Javanese Thin Tail and Chinese Hu and Han breeds (Notter, 2008). This presents an opportunity for the use of these breeds in regional crossbreeding programs aimed at increasing fecundity. Crossbreeding and gene introgression programs using prolific breeds have proven their ability to increase fecundity and BW of offspring weaned per female for each gestation.

Nutritional Flushing

The provision of additional dietary energy at the onset of the breeding season (nutritional flushing) and introduction of males (male effect) are strategies to induce the beginning of cyclicity early in the breeding season in small ruminants (Fitz-Rodríguez et al., 2009; Talafha and Ababneh, 2011). This can be accomplished in low input agriculture by managing the exposure of females to males, by holding some higher quality pasture in reserve to be used at the onset of the breeding season, or by the provision of grain 2 to 3 wk before and into the breeding season. With such nutritional strategies, improvements in the ovulation rate of 0.5 to 1 have been reported (Naqvi et al., 2012). The combined use of early introduction of males and flushing increased the number of females conceiving early in the breeding season. However, effects reported by others have been variable (De Santiago-Miramontes et al., 2011). These strategies are most effective when the animals are not overly fat (e.g., are thin).

Early Weaning

To maintain a yearly calving interval, beef cows must rebreed within approximately 85 d of parturition. The suckling stimulus can delay or completely suppress cyclicity in beef females, especially when nutrition is inadequate (Crowe, 2008). Sucklinginduced anestrus is thought to result from direct endocrine suppression induced by suckling and the increased metabolic demands of lactation. In systems with sufficient feed and management resources, early weaning is an effective method for the induction of cyclicity and rebreeding (Zi, 2003; Crowe, 2008). In management systems that cannot support early weaning, intermittent weaning can be used. For example, 12 h temporary weaning of Bos indicus cattle improved conception rates in extensively managed cows (Escrivão et al., 2009). To maximize fertility in swine production, females should achieve puberty at an early age, be inseminated with high-quality semen at their pubertal estrus, farrow a large litter, lactate for 3 to 4 wk, wean that litter, and then return to estrus and be rebred within 4 to 8 d (Kirkwood and Thacker, 1992).

Enhanced Periparturient Care and Health

There is a clear positive relationship between health and fertility in farm animals (Weigel, 2006). The most significant risk for disease for any female animal is during the periparturient period (Beever, 2006; Thatcher et al., 2006; Gumen et al., 2011). Postpartum disease results in delayed resumption of ovarian activity and longer days between births resulting in poor fertility (Thatcher et al., 2006). Indeed, low fertility accounts for roughly one-third of the voluntary culling decisions in North American dairy systems (Beever, 2006; Thatcher et al., 2006; Gumen et al., 2011). Successfully navigating the transition period in dairy cows involves careful attention to the metabolic status of cows in the pre and postpartum periods. The length of the dry period could be reduced to less than 60 d, and in fact, recent work suggests a dry period of 30 d may result in better metabolic profiles and reproductive health in the postpartum period (Gumen et al., 2011).

However, difficulties that arise in managing cows with little to no dry period may limit the application of this strategy. Another strategy to optimize metabolic function during the dry period is to increase the roughage content while simultaneously reducing energy in the diet (Beever, 2006). This results in increased DMI and fewer metabolic problems during early lactation. In developed countries, manipulating the composition of dietary fats has yielded improved reproductive performance. For example, current recommendations are to feed a diet enriched in omega-6 fats (pro-inflammatory) in the immediate peripartum period and then switch to omega-3 fats (anti-inflammatory) at 30 d postpartum to promote pregnancy establishment (Thatcher et al., 2006; Silvestre et al., 2011). In addition, genetic selection for resistance to diseases and metabolic disorders should yield improvements in health during the periparturient period (Weigel, 2006).

The health of animals is affected by many aspects of the production system, particularly nutrition, stress, facilities, and preventive health measures (vaccination and quarantine of new arrivals). For optimal fertility, dams should receive additional care and optimal nutrition during the period immediately before and after parturition. Animals should be vaccinated and receive appropriate boosters for endemic diseases, especially diseases that can cause early embryonic mortality and abortion. Animals diagnosed with the disease should receive prompt medical care; however, this is not always the case. In smallholder dairy farms in Malawi, 11% of farmers reported that they did not treat sick cows due to a lack of available drugs or the high cost of drugs (Banda et al., 2011). Failure to effectively control the disease is exacerbated by poor recordkeeping and a lack of postmortem disease diagnosis in developing countries.

Reduction of Stressors

Environmental stressors (heat, transport, predation, feed, and water contamination, etc.) have been shown to cause embryo loss, especially in the first 4 to 6 wk after mating and insemination (Hansen and Block, 2004). Management strategies can reduce stress during early gestation. The provision of adequate access to shade and water can reduce heat stress and minimizing transport or herding of animals over long distances during the first 4 to 6 wk of gestation.

Assisted Reproductive Technologies

Artificial insemination and other reproductive technologies (estrus synchronization, embryo transfer, and gender-selected semen; De Vries et al., 2008) can be used to enhance the genetic value of offspring, particularly relative to fertility traits. For example, AI improved several measures of fertility compared to natural mating when implemented as a program to improve the efficiency of smallholder swine production in Thailand (Visalvethaya et al., 2011). In addition, 55% of smallholder dairy farmers in Malawi reported using AI (Banda et al., 2011). However, the success of AI programs was dependent on the distance from access to semen, good quality equipment, training of inseminators, heat detection skills, general education level, and even age of the farmer. These results suggest the potential for improvement in fertility with enhanced educational efforts and small investments in the AI infrastructure. Hormonal injection programs designed to synchronize estrus or ovulation are credited, in part, with the apparent reversal of declining fertility seen in North American dairy systems during the last decade.

These programs have aided larger farms in dealing with the difficulty of accurately detecting estrus in cattle. The result has been more cows submitted for insemination and higher pregnancy rates (Gumen et al., 2011). The use of these technologies is limited in small ruminants due to their cost, especially in developing countries. Reproductive management protocols for optimal fertility must include timely and accurate determination of pregnancy status so that decisions can be implemented to cull or re-inseminate females. A minority of smallholder farmers in Malawi (23%) reported using pregnancy diagnosis, but this generally occurred 90 d after insemination, precluding the timely re-insemination of cows that failed to conceive (Banda et al., 2011). The typical method was transrectal palpation, but other widely used methods for determining pregnancy status included failure to return to estrus and physical appearance. These latter approaches are associated with large errors, particularly if farmers have few cows, and they are housed individually (nongrazed) as is often the case.

Conclusion

Increasing animal productivity can be a very successful strategy for mitigating GHG emissions from the ruminant sector in both developed and developing countries, with more significant mitigating potential in developing countries. Improving forage quality, grain inclusion in the diet, achieving the genetic potential of the animal for production through proper nutrition, and the use of improved local breeds and/or of crossbreeds are recommended approaches for improving animal productivity and reducing GHG emissions per unit of product. Selection for high productivity should not be at the expense of other important traits such as reproduction and animal health. Enhanced animal productivity and feed efficiency with metabolic modifiers, such as rbST and growth promotants, would reduce GHG Ei. Still, the applicability of these mitigation practices is limited to regions where the use of these compounds is permitted and where feed, facility, and management resources are available to meet the needs of high productivity.

Improved animal health and reduced mortality and morbidity are expected to result in increased animal productivity, diluting GHG emissions per unit of product. Mitigation options that enhance the nutritional value of low-quality feed in ruminant diets could have a beneficial effect on individual animal productivity, which, provided that the total herd size is not increased (and preferably is reduced), will increase herd productivity while keeping herd CH4 output constant. Consequentially, CH4 Ei will be decreased. The reduction of the herd size itself can result in the concomitant decrease of herd CH4 emission and increased herd productivity as better feed materials are fed to animals. Constraints to applying mitigation options such as chemical treatment, supplementation, breeding, and selection for straw quality, and reduction of herd size are mainly economic and sociocultural. Suggestions to overcome these constraints have been discussed in FAO (2011b). Technically, these treatments can easily be applied.

However, despite a long history of research to treat low-quality feeds, there has been little adoption of these practices on farms. The potential of using RFI as a selection tool for low CH4 emitters is an interesting mitigation option. Still, there is little evidence that low-RFI animals have lower CH4 emissions per unit of feed intake or product. Therefore, the immediate gain in GHG reductions through RFI is considered uncertain. However, selection for feed efficiency will yield animals with lower GHG Ei. Breed differences and maximum utilization of the genetic potential of the animal for feed conversion efficiency can be powerful GHG mitigation tools in both ruminants and nonruminants. Reducing age at harvest and the number of days cattle are on feed in the feedlot can have a significant impact on GHG emissions in beef and other meat animal production systems. Pursuing a suite of intensive and extensive reproductive management technologies provides a significant opportunity to reduce GHG emissions.

Recommended approaches will differ by region and species but should target increasing conception rates in dairy, beef, and buffalo, increasing fecundity in swine and small ruminants and reducing embryo mortality in all species. The result will be fewer replacement animals needed, fewer males required where AI is adopted, longer productive life, and higher production per breeding animal. We want to proceed further, more in-depth on this controversial subject. Therefore, please follow us on social media and join us on the (15^th) fifteenth of the month for Part (2!) two to learn more about the environmental impact of beef production. 

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