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Management Issues With Dry Cows and a New Feeding System for Improved Health, Welfare and Performance

21 May 2013

Periparturient cows showed a three fold decrease in vet costs after being given high energy diets, says David Beever, a consultant from Ireland, who gathered evidence from 270 dairy farms finding that culling rate, weight loss and fertility all improved.

Introduction

From the cow’s perspective, the dry period presents an opportunity for metabolic recovery following the demands of the previous lactation. While foetal growth rate increases exponentially at this time, total nutrient requirements of the cow remain relatively low, a summation of cow maintenance, advancing foetal growth and tissue regeneration, including the udder.

Many farmers view the dry period as an opportunity to reduce management inputs, with less attention given to the cow’s nutritional and welfare needs. This is certainly the case on many farms during the first part of the dry period, known as the ‘far-off’ period, where interventions can be minimal.

This is followed by the ‘close-up’ period when, leading up to calving, most farmers increase ration nutrient density and feeding rate. This practice, based on recommendations by nutritionists or historical practice, aims to “steam-up” the cow in anticipation of her increased nutrient demands after calving. Despite extensive adoption of this approach, there is surprisingly little research evidence supporting its efficacy (Drackley & Dann, 2008).

Many farms continue to experience high incidence rates of periparturient issues, compromised feed intakes after calving and increased body condition loss, with associated effects on fertility, all of which have welfare implications.

This paper reviews these issues and presents an alternative dry cow feeding system which is gaining considerable success as demonstrated by field data and recent research (Richards et al., 2009).

In this respect, Cunningham (2004) concluded that today’s dairy cows, often with significantly improved genetic potential to produce milk, are inherently no less fertile or more prone to production-related diseases than the cows they have replaced. Rather, it is the way cows are managed, especially their nutritional management, that is contributing to many of the health and welfare problems occurring on dairy farms.

Fertility

Overall fertility of dairy cows is declining across the world (Butler & Smith, 1989; Smith & Wallace, 1998), evident in both high (Beever et al., 1999) and low yielding herds, including pasture-based cows (Mee, 2004).

Records indicate a progressive one percent unit annual decline in first service conception rate, requiring more breeding events to establish a successful pregnancy (Royal et al., 2000). This inevitably increases calving intervals, a major issue in spring-calving herds, where tight calving patterns are targeted to meet the spring grass flush.

It also increases the dry period, of concern to householder herds with low cow numbers where there is high reliance on income from daily milk sales. Infertility remains the major reason for premature culling of cows, impacting adversely on lifetime milk production. Recent estimates suggest UK dairy cows complete an average of 3.3 lactations before culling, contrasting with 4.8 lactations in 1975. The position is worse in the United States. Collectively, poor fertility through lost production, lost opportunities and lost cows add significantly to the overall costs of milk production (Beever, 2004).

Genetics, management and nutrition can all be contributory factors to declining fertility. Over recent years, significant herd consolidation has occurred in many countries, with fewer herds and larger herd sizes.

With more cows being managed per available staff member, and a declining availability of qualified dairy staff, many cows now receive less individual attention, which may have contributed to the decline in fertility. Further to this, most dairy businesses have experienced only modest financial returns over the last 15 years or so; Colman et al. (2004) reported that 60 percent of all milk sold by UK farmers in 2002 incurred a net financial loss.

As a consequence, infrastructure investments have declined, leading too many farms with inadequate cubicles, poor feed and water facilities, inadequate lighting and poor walking surfaces, all impacting negatively on cow welfare and performance.

Against this, there have been significant advances in ruminant nutrition science, with many of these findings now embodied in sophisticated rationing systems for dairy cows. But the standard of dairy cow nutrition provided for and adopted by many herds has not progressed at the same rate, with many farms still failing to meet the more exacting demands of the modern dairy cow. Over-dominance by the feed trade, with over-reliance on purchased concentrates and reduced recognition of home grown forages and feeds, has contributed to this effect.

It is argued that the declining fertility which many herds are experiencing has an important underlying nutritional element. With closer attention to the nutritional needs of the dry cow, significant improvements in herd fertility could be achieved, without recourse to major interventions including expensive veterinary products or a possible breed change. Improved management of the cow during the dry period has the potential to improve overall cow wellbeing and longevity.

Body Condition (BC)

Significant loss of body energy may occur in early lactation if feed intake or the efficiency with which that feed is digested by the cow fails to meet the demands of milk production (Bauman & Currie, 1980, Veerkamp & Emmans, 1995). Villa-Godoy et al. (1988) concluded that energy intake was the main factor contributing to body energy loss in early lactation, while Veerkamp & Brotherstone, (1997) argued that increased milk yield was a more pronounced determinant of BC loss.

Over-feeding of protein in early lactation, often to stimulate milk production, can increase BC loss. Meanwhile, a suboptimal supply of protein can affect both feed intake and digestive efficiency, both of which can promote body condition loss as the cows’ potential to produce milk prevails.

The rumen is the key driver of feed intake and efficient feed utilization, both of which can significantly affect overall cow performance. Data with pasture-fed cows led Buckley et al. (2003) to conclude that “reproductive performance, especially the probability of conception, may be negatively associated with the magnitude and duration of negative energy balance in early lactation”.

Previously, Butler & Smith (1989) showed cows losing between 0.5 and 1.0 BC score units between calving and first service had a mean pregnancy rate to that service of 53 percent compared with only 17 percent for cows losing over 1.0 BC score at this time. Subsequently, Beam & Butler (1999) reported that increased negative energy balance reduced the pulse frequency of luteinizing hormone (LH), with a direct impact on the subsequent fate of the developing follicle.

Meanwhile, Mee (2004) noted that between 1991 and 1998, first service conception rate in pasture fed cows declined from 60 percent to 54 percent while the calving interval increased by 10 days and the number of cows experiencing abnormal cycles increased from 13 percent to 26 percent. Mee (2004) also noted less overt oestrus behaviour in many cows, concluding that “strategies are required to improve or halt the decline in reproductive performance (and that) these must include feeding systems to reduce negative energy balance and maintain body condition”.

Hattan et al. (2001) examined the performance of average yielding (AYC; 8 000 litre) and high yielding (HYC; 11 000 litre) cows. From a pre-calving BC score of 2.9, AYC lost an average 0.8 BC score over the first five weeks of lactation, followed by a period of reasonable stability and then modest gains as lactation advanced.

In contrast, HYC, with a similar pre-calving BC score, showed a deeper and more extended BC loss through to week 11 and an average BC score of 1.6. Thereafter, the BC score remained relatively stable until the study terminated at lactation week 24, by which time the BC score differed by 0.7 between the two groups.

Parallel studies of energy metabolism (Beever, 2003) estimated 60 kg loss in body fat by lactation week 11 in HYC, with a net gain of 28 kg body fat between weeks 21 and 30. Thus by 210 days in milk, these cows had only replenished 55 percent of the body fat lost during early lactation.

With lower yielding cows fed more modest rations and lower peak milk yields, Sutter & Beever (2000) determined a negative energy balance in lactation week 1 equivalent to 3.2 kg body tissue/day, declining to 1.7 kg/day between weeks 2 and 4, and further to 1.1 kg/day, but the cows were still in negative energy balance when the study terminated at lactation week 8. Mobilized tissue over the first eight weeks of lactation was sufficient to support the production of 300 litres of milk, from a total recorded production over that period of 1820 litres.

It is concluded that in many cows the extent of body condition loss in early lactation can be quite severe. As Veerkamp & Brotherstone (1997) indicated, this may be driven by the increased potential of many cows to produce high volumes of milk, but equally the importance of optimizing energy intake in early lactation as considered by Bauman & Currie (1980) and Veerkamp & Emmans (1995), cannot be overlooked.

In this respect, the relative amounts of adipose tissue in the periparturient cow may be important and where cows have increased fat deposits this may lead to depressed appetites after calving. Loss of BC per se is not necessarily a welfare issue, unless the cow becomes seriously debilitated, but the knock-on consequences for the cow and the farmer can be quite severe.

Fat Metabolism in Lactating Dairy Cows

Where the extent of fat mobilization approaches 60 kg during early lactation, it is not surprising that Reynolds et al. (2003) reported major changes in the hepatic flux of nonesterified fatty acids (NEFA) as cows progressed from late pregnancy into lactation. Prior to calving, NEFA flux to the liver was relatively stable, equivalent to 1 mole palmitate/day. However, after 11 days post-calving, this had increased to over 5.5 moles palmitate/day, declining gradually thereafter as lactation progressed, even though it still remained at twice the pre-calving baseline by lactation week 10.

The liver is the major site of fat metabolism and under normal conditions significant amounts of NEFA will be oxidized to support the cow’s energy requirements. Alternatively, and especially when hepatic NEFA load is increased, NEFA may be exported from the liver as very low density lipoproteins (VLDL), to be metabolized in other tissues.

In this way, significant amounts of mobilized body fat support the synthesis of milk fat, especially during early lactation when feed intake fails to match milk output. But when normal oxidative or transport capacities of the liver are exceeded, NEFA are either partially oxidized, with an associated rise in plasma ketones, or accumulate within liver cells.

Drackley (1999) suggested that the rate of fat deposition in the liver may approach 500 g/day during early lactation and, if maintained, would be sufficient to fully saturate liver cells with fat within two weeks. This will inevitably affect other hepatic functions. Strang et al. (1998) reported a negative linear relationship between cellular fat concentrations and rate of conversion of ammonia into urea. They added that up to 60 percent of dairy cows may have liver fat levels in excess of 10 percent on day 1 postpartum, sufficient to cause a 20 percent reduction in the rate of urea and glucose production by the liver.

Meanwhile, a survey from Michigan State University of over 1 500 cows found positive relationships between periparturient NEFA levels and the incidence of dystocia, retained foetal membranes, mastitis, ketosis and displaced abomasums, all of which are potential welfare issues. Added to which, Wathes et al. (2003) noted that both BC at calving and extent of BC loss post-calving affected the interval to a successful conception, with a higher loss of BC associated with reduced circulating IGF-1 levels.

Further, cows with extended inter-luteal intervals or prolonged anoestrus (usually after an oestrus event) had higher levels of NEFA and ß-hydroxy butyrate (BHB), both indicative of increased BC loss. Kruips et al. (2001) found significant relationships between plasma NEFA and liver triacylglycerol levels and the interval to first ovulation in cows that were deliberately over-conditioned prior to calving.

It is concluded that cows showing excessive BC at calving, as well as high rates of BC loss after calving, are likely to be more difficult to rebreed, and have more metabolic issues during the periparturient period. In turn these events can impact negatively on animal welfare and longevity.

Controlled-Energy High-Fibre Feeding Strategy

Contrary to popular belief, dry cows do not limit feed intake to their nutrient, especially energy, requirements. With sufficient opportunity, they may consume as much as 70 percent excess, resulting in increased body fat deposition. After calving, this additional energy will be used to support milk production, with an associated reduction in feed intake. Further, recent scientific evidence suggests that nutritional management of the dry cow during the far-off period may be as important as it is considered to be during the close-up period.

Tackling both issues, a novel strategy of controlled energy feeding during the whole dry period has been developed, and shown to bring significant improvements in cow health during the periparturient period and subsequent lactational performance, with obvious gains in animal welfare.

In a cohort of over 600 000 cows removed due to death or culling from 6 000 herds over five years, Fetrow et al. (2006) found that 25 percent left within the first 60 days after calving. This represents a serious waste of animal and financial resources, given the accrued costs of breeding, gestation feeding and calving against a significant loss of the cow’s potential to produce milk during that lactation. Such premature losses also impact on lifetime milk production, while clearly having important welfare implications. It is argued that a significant part of this loss could be averted by improved nutritional management of the dry cow.

Dann et al. (2006), Douglas et al. (2006) and Janovick & Drackley (2010) have shown that excess energy intake, even in dry cows of low to average BC, can predispose health and welfare issues around calving and the early post-calving period, including dystocia, fatty liver and ketosis. Part of the rationale behind increased energy feeding prior to calving was the notion that the cow’s appetite generally declines as calving approaches. But Grummer et al. (2004) Richards et al. (2009) and Janovick & Drackley (2010) have argued that the decline in dry matter intake is more closely related to ration energy density.

Beever (2006) and Drackley & Dann (2008) proposed a feeding system to control energy intake during the dry period, while at the same time ensuring that all other nutrient requirements are met. A ration with high levels of bulky forage, including significant amounts of cereal straw and restricted amounts of the intended lactation forages and concentrates is recommended.

Pasture availability of grazing cows should be limited and an alternative forage containing less potassium (e.g. maize or cereal silage) provided. With high levels of cereal straw, total ration energy density is reduced (circa 9 MJ of ME/kg of DM), but achieved DM intakes of the total ration approaching 12 kg/day are sufficient to meet the energy requirements of some of the largest dairy cows.

A typical ration formulation for housed cows would be 50 percent cereal straw, 30 percent lactation forages and 20 percent lactation concentrates (DM basis), with a suitable dry cow mineral. This ration is fed throughout the whole dry period, abandoning the historical far-off/close-up approach.

Central to this strategy, however, is feed presentation. Providing cereal straw as a separate feed is no guarantee that cows will consume the requisite amount of this feed to reduce overall consumed energy density. Cows naturally select more palatable feeds if given the opportunity, thus defeating the overall objective to lower ration energy density. Consequently all forages and concentrates should be provided as a mixed ration, with forage length suitably processed to ensure minimal feed selection while retaining essential physical structure to optimize rumen function. This can be achieved with suitable ration mixing equipment but as Humphries et al. (2010) showed, some feed mixing systems are considerably more suitable for producing well-mixed rations that minimize feed selection and optimize physical fibre content.

Colman et al., (2011) presented evidence of the impact of adopting a controlled-energy high-fibre (CEHF) mixed ration feeding system for dry cows. Prior to adoption of the CEHF system, a cohort of 277 dairy farms in France, Ireland, Sweden and the United Kingdom, with over 27 000 cows, averaged 45.5 health issues per 100 cows around the calving period, including assisted calvings, retained foetal membranes, milk fever, displaced abomasums and ketosis.

All of these can be considered as potential welfare issues, of which milk fever can be particularly debilitating while in some cases, displaced abomasums can be life-threatening. Six months after adoption of CEHF, overall incidence rate had declined to 16.2 cases per 100 cows, with over 75 percent reductions in milk fever, ketosis and displaced abomasums, and more recent field data have confirmed the potential of this approach to reduce periparturient health and welfare issues in dairy cows.

Supporting scientific evidence for CEHF feeding throughout the whole dry period has been provided by Richards et al. (2009). Three treatments, all fed ad libitum, comprised (i) CEHF, from drying-off until calving, with 40 percent (DM basis) wheat straw inclusion; (ii) control, a moderate-energy diet fed from drying-off until calving; and (iii) a 2-stage system with CEHF fed from drying-off until 21 days prepartum, followed by control until calving.

Noticeably, control cows consumed high levels of feed until week 4 before calving, after which a sustained reduction was noted. On the other hand, CEHF cows had lower but more stable intakes through to calving. Initially 2-stage cows behaved as CEHF cows but, following the ration change, there was an immediate feed intake increase before declining in line with control cows through to calving. Feed intakes post-calving were improved on CEHF with a slower increase noted for control cows.

As expected, control cows gained BC prior to calving followed by an accelerated loss, while CEHF and 2-stage cows showed minimal change during the dry period, with substantially reduced losses thereafter and all treatments were largely indistinguishable by lactation week 10 with respect to BC. CEHF cows showed a slightly slower rise in milk production, although this was not apparent in first calvers.

However there were notable changes in plasma NEFA and BHB levels. While NEFAs increased during the calving period on all treatments, CEHF cows showed a much reduced peak compared with control cows, while 2-stage cows showed some attenuation of this increase. Further, levels were still elevated at lactation day 40 in control cows with CEHF and 2-stage cows showing much earlier returns to base levels (15 and 20 days respectively). Changes in BHB were even more pronounced: base levels restored by day 10 in CEHF cows compared with day 16 in 2-stage cows, while levels were still elevated at day 60 in control cows. Supporting evidence showed that control cows had significantly higher levels of fat accumulation in the liver than 2-stage and especially CEHF cows, while changes in plasma insulin levels strongly suggested that control cows were experiencing insulin resistance, which in other studies has been shown to affect fertility adversely.

Assessment of the impact of any management changes on dairy cow fertility requires dedicated longitudinal studies involving extensive measurements on a large number of cows. Neither Colman et al. (2011) nor Richards et al. (2009) provided such data and thus conclusive evidence of the possible benefits of the CEHF strategy on fertility is not available. However many of the responses noted above, especially improved metabolic health and reduced body condition loss, can be advanced as factors likely to contribute to fewer cows experiencing reproductive issues. There is considerable anecdotal evidence to support this claim, with clear indications of their effect on cow welfare and longevity.

In summary, and beyond any perceived improvement in fertility, data obtained from the above research and on-farm studies provides convincing evidence that controlling energy intake during the whole dry period to meet but not exceed the animal’s requirements results in significant improvements in cow health and welfare around the calving period, and prepares the cow for a more successful lactation and hopefully a less arduous breeding event. The welfare benefits of this approach should be self-evident to the reader and are most obvious when seen on-farm.

In addition, the CEHF system brings important monetary gains through reduced interventions (and associated veterinary costs) and improved lactational performance. For those herds involved in the study, and using industry-accepted guideline costs, it was estimated, that before intervention compromised health around the calving period amounted to over €9 500/year for a 100 cow herd (€95/cow), reduced to €3 200/year after adoption of CEHF. This difference could be worth an additional 1.1 cents for every litre of milk produced for an average yielding herd.

Conclusion

There is clear evidence that metabolic and health issues around the calving event impact negatively on cow welfare and farm profitability. The current system of far-off/close-up feeding has failed to deliver the expected gains, with many farmers seeking expensive interventions, and general cow welfare showing no substantial improvement. The CEHF system, backed by research and farm evidence, is simple to execute and has been shown to overcome many of the health and welfare issues experienced by many cows around the calving period. However, the importance of ration presentation to avoid ration selection and promote optimal rumen function cannot be overemphasized if the desired gains are to be achieved.

References

Bauman, D.E. & Currie, D.B. 1989. Partitioning of nutrients during pregnancy and lactation: a review of mechanisms involving homeostatis and homeorhesis. J. Dairy Sci. 63: 1514–1529.

Beam, S.W. & Butler, W.R. 1999. Effects of energy balance on follicular development and first ovulation in post-partum dairy cows. J. Reprod. Fertil. 54(Suppl): 411–424.

Beever, D.E. 2003. Managing dairy cows for optimal performance. In J.L. Corbett, ed. Recent Advances in Animal Nutrition in Australia 2003. University of New England, Armidale, NSW, Australia, Animal Science.

Beever, D.E. 2004. Opportunities to improve the performance and profitability of dairy farms through better nutrition. In Knowledge Agriculture, ‘Perspectives Towards a new Model of Milk Production’, pp. 6–8. Co Carlow, Ireland, R Keenan & Co.

Beever, D.E. 2006.The impact of controlled nutrition during the dry period on dairy cow health, fertility and performance. Anim. Reprod. Sci. 96: 212–226.

Beever, D.E., Hattan, A.J., Reynolds, C.K. & Cammell, S.B. 1999. Nutrient supply to highyielding dairy cows. In M.G. Diskin, ed. Fertility in the High Producing Dairy Cow. BSAS Occasional Symposium No 26, Vol 1. Galway.

Buckley, F., O’Sullivan, K., Mee, J.F., Evans, R.D. & Dillon, P. 2003. Relationships among milk yield, body condition, cow weight and reproduction in spring-calved Holstein-Friesians. J. Dairy Sci. 86: 2308–2319.

Butler, W.R. & Smith, R.D. 1989. Interrelationships between energy balance and postpartum reproductive function in dairy cattle. J. Dairy Sci. 72: 767–783.

Colman, D., Farrar, J. & Zhuang, Y. 2004. Economics of milk production England and Wales, 2003. Farm Business Unit, School of Economic Studies, The University of Manchester.

Colman, D.R, Beever, D.E., Jolly, R.W. & Drackley J.K. 2011. Gaining from Technology for Improved Dairy Cow Nutrition: Economic, Environmental, and Animal Health Benefits. Professional Animal Scientist 27: 505.

Cunningham, E.P. 2004. The genetic dimension. In Knowledge Agriculture, ‘Perspectives Towards a new Model of Milk Production’, pp. 9–11. Co Carlow, Ireland, R Keenan & Co.

Dann, H.M., Litherland, N.B., Underwood, J.P., Bionaz, M., D’Angelo, A., McFadden, J.W. & Drackley, J.K. 2006. Diets during far-off and close-up dry periods affect periparturient metabolism and lactation in multiparous cows. J. Dairy Sci. 89: 3563–3577.

Douglas, G.N., Overton, T.R., Bateman II, H.G., Dann, H.M. & Drackley, J.K. 2006. Prepartal plane of nutrition, regardless of dietary energy source, affects periparturient metabolism and dry matter intake in Holstein cows. J. Dairy Sci. 89: 2141–2157.

Drackley, J.K. 1999. Biology of dairy cows during the transition period|: the final frontier? J. Dairy Sci. 82: 2259–2273.

Drackley, J.K. & Dann, H.M. 2008. A scientific approach to feeding dry cows. In P.C. Garnsworthy and J. Wiseman, eds. Recent Advances in Animal Nutrition, pp. 43–74. Nottingham University Press, UK.

Fetrow, J., Nordlund, K.V. & Norman, H.D. 2006. Invited review: Culling: Nomenclature, definitions, and recommendations. J. Dairy Sci. 89: 1896–1905

Grummer, R.R., Mashek, D.G. & Hayirli, A. 2004. Dry matter intake and energy balance in the transition period. Vet. Clin. Food Anim. 20: 447–470.

Hattan, A.J., Beever, D.E., Cammell, S.B. & Sutton, J.D. 2001. Proceedings of 15th EAAP Energy Symposium, Copenhagen
.
Humphries, D.J., Beever, D.E. & Reynolds, C.K. 2010. Adding straw to a total mixed ration and the method of straw inclusion affects production and eating behaviour of lactating dairy cows. Adv. Anim. Biosci. 1: 95.

Janovick, N.A. & Drackley, J.K. 2010. Prepartum dietary management of energy intake affects postpartum intake and lactation performance by primiparous and multiparous Holstein cows. J. Dairy Sci. 93: 3086–3102.

Kruip, T.A.M., Wensing, T. & Vos, P. 2001. Characteristics of abnormal perperium in dairy cattle and the rationale for common treatments. British Society of Animal Science, Occasional Publication 26: 63–80.

Mee, J.F. 2004. Temporal patterns in reproductive performance in Irish dairy herds and associated risk factors. Irish Vet. J. 57(3): 158–166.

Reynolds, C.K., Aikman, B.C., Lupoli, B. & Humphries, D.J. 2003. Splanchnic metabolism of dairy cows during the transition from late gestation through early lactation. J. Dairy Sci. 86: 1201–1217.

Richards, B.F., Janovick, N.AA., Moyes, K.M., Beever D.E. & Drackley, J.K. 2009. Comparison of a controlled-energy high-fiber diet fed throughout the dry period to a two-stage far-off and close-up dietary strategy. J. Dairy Sci. 92(E. Suppl. 1): 140(Abstr.).

Royal, M.D., Darwash, A.O., Flint, A.P.F., Webb, R., Woolliams, J.A. & Lamming, G.E. 2000. Declining fertility in dairy cattle: changes in traditional and endocrine parameters of fertility. Anim. Sci. 70: 487–501.

Smith, M.C.A. & Wallace, J.M. 1998. Influence of early postpartum ovulation on the re-establishment of pregnancy in multiparous and primaparous dairy cattle. Reprod. Fert. Develop. 10: 207–216.

Strang, B.D., Berics, S.J., Grummer, R.R. & Armentano, L.E. 1998. Effect of long chain fatty acids on triacylglyceride accumulation, gluconeogeneisis and ureagenesis in bovine hepatocytes. J. Dairy Sci. 81: 728–739

Sutter, F. & Beever, D.E. 2000. Energy and nitrogen metabolism in Holstein-Friesian cows during early lactation. Anim. Sci. 70: 503–514.

Veerkamp, R.F. & Brotherstone, S. 1997. Genetic correlations between linear type traits, feed intake, liveweight and condition score in Holstein Friesian dairy cattle. Anim. Sci. 64: 385–92.

Veerkamp, R.F. & Emmans, G.C. 1995. Sources of genetic variation in energetic efficiency of dairy cows. Livest. Prod. Sci. 44: 87–97.

Villa-Godoy, A., Hughes, T.L., Emery, R.S., Chaplin, L.T. & Fogwell, R.L. 1988. Association between energy balance and luteal function in lactating dairy cows. J. Dairy Sci. 71: 1063–1107.

Wathes, D.C., Tayler, V.J., Cheng, Z. & Mann, G.E. 2003. Follicle growth, corpus luteum function and their effects on embryo development in postpartum dairy cows. Reprod. Suppl. 61: 219–237.

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