INCREASING INFERTILITY IN CROSS BREED DAIRY COWS IN INDIA: EMERGING PROBLEM & SOLUTION
BY- DR. RAJESH KR. SINGH, LIVESTOCK & POULTRY CONSULTANT,
9431309542
Currently farmers, veterinarians, consultants and even researchers are very demanding for our dairy cows. Besides the demand to produce lots of milk containing high levels of protein, we want them to calve each year. The latter implies that we like every dairy cow to be pregnant or to be recovering from pregnancy and preparing for a new pregnancy at all times, which makes fertility a full time job for her.
Suboptimal reproductive performance is one of the main factors responsible for the economic losses in large dairy farms. Milk production per cow has steadily increased through the combined improvement of management, nutrition, and genetic selection actions. However, farms are becoming larger and with more productive cows, increasing the challenge of maintaining reproductive efficiency in increasingly adverse situations due to metabolic adaptations for this purpose . Thus, it is justified to maintain the most demanding reproduction at satisfactory levels, considering that high producing cows have a higher incidence of infertility or subfertility . However, in addition to milk production, other factors are likely to decrease reproductive efficiency in these herds.
India total cattle population is 190.9 million, out of which adult female cow population is 76.7 million (19th Livestock Census). So, the number of quality, high yielding cows is less and management of dairy cow fertility is now becoming a more critical part of a dairy farm. However, it is a real concern when farmers become so concerned about fertility that they resort to management decisions that affect their profitability. The stress of high milk production, along with increasing herd size and changes in facilities and management, has made fertility one of the main focuses of genetic improvement today. Because there is a positive correlation between milk yield and days open, the task of improving fertility while selecting for high milk production is challenging. Fertility of lactating dairy cattle has declined throughout much of the world in the last fifty years or so although accompanied by large increases in milk yield, the reduction in fertility has not been simply due to higher milk production. Indeed, estimates of the relationship between milk yield and fertility vary from negative to positive (Eicker et al., 1996; Loeffler et al., 1999; García Ispierto et al., 2007; Caraviello et al., 2006; LópezGatius et al., 2006; Demetrio et al., 2007). Fertility in cattle has many pre-requisites and components, which require males and females to be functionally capable of reaching the last step, the birth of a normal, vital calf, thus defining the general breeding goal: cows should return to normal cyclicity early postpartum, show strong and regular estrus signs, conceive after AI, carry their pregnancy to term, calve easily and give birth to viable and healthy calves. Low calving rates relate to the inability of the cow to resume ovarian activity and thus failure to cycle and to express estrous signs (anovulatory and behavioral anestrus, irregular estrous cyclicity, etc); as well as to reproductive wastage due to fertilization failure, early and late embryonic mortality, foetal mortality (abortions) and stillbirths. Fertilization rates (% of ova being fertilized), are generally high after AI under controlled conditions. However, decreasing rates are now seen in high producing cows. There are probably many causes why 10 – 25% of ova are not fertilized after AI, and they can be of either male or female origin. Many studies have reported a decrease in the fertility of dairy cows. This situation is widespread since the studies have originated in regions all over the globe. The conception rate at first A.I. has decreased by 0.45% in U.S (Butler and Smith, 1989; Beam and Butler, 1999) and by 1% in England (Royal et al., 2000a; Royal et al., 2000b) per year over a twenty year period. The goal of this article is to review the various factors associated with decreasing fertility and specially management factors.
Indicators of fertility
In the evaluation of reproduction it is important to differentiate between the concepts of reproductive performance, which is defined as the female’s ability to produce a live calf, and is affected by foetal development, calving and calf survival. Reproductive performance is calculated using various indicators such the number of days open (the interval between calving and successful AI) or the inter-calving periods. These two indicators are influenced by cow fertility as well as by other herd management factors, like heat detection and the length of the voluntary waiting period (interval between calving and time to first AI). For an adequate evaluation of bovine fertility, we need to refer to certain standards (Esslemont and Kossaibati, 2000). Cow fertility is generally evaluated by the conception rate (CR), defined as the proportion of cows declared pregnant following AI. This indicator is inversely related with the number of AIs per conception. Artificial insemination centres use indicators calculated from available data. In general, they use the Non Return Rate (at day 56 or 60.) This corresponds to the proportion of AI without a second AI within a predetermined period. In the United States, bull fertility is evaluated using the ERCR (Estimated Relative Conception Rate). It may be interpreted as being the NRR at 70 days of the AIs performed using a bull in relation to that of the other bulls used for the same herd. In this case, factors such as the age of the cow, lactation stage and milk production are taken into consideration for the calculation.
Factors influencing fertility of cows:———-
1. Age of the cows –
Analysis of fertility data demonstrates unequivocally that decreased fertility is associated with lactation number in cows. A study undertaken by Bouchard and DuTremblay (2003) between 1993 and 2002 on 60,000 cows/year from 2000 dairy farms shows no change in conception rate at first AI and second AI in heifers. However, an important decrease was observed in multiparous cows, including primiparous cows. The same trend was demonstrated in AI centres in Canada and the United States (Fricke, 2002; Van Doormaal, 2002). Data collected from embryo transfers, even though they are performed under different conditions than regular AIs, show the same influence of age on cow fertility. An analysis of data collected from 2809 embryo harvests performed after insemination with semen from six of the most frequently used bulls shows that:
1) the percentage of unfertilized ova in collections performed on primiparous cows is twice that of heifers; and 2) the percentages of unfertilized ova and degenerated embryos of the total embryo/ ova collected increases with the age of the cows (Gestion des récoltes, Québec, 2003).
2. Production and nutrition-
All reports have shown an association between an increase in milk production over the years and a decrease in fertility (Lucy, 2001.) The Quebec study of dairy herds shows that in comparison to cows whose production is less than 7500 kg, CR1 decreases by 7.8% in cows who produce 7500-10,000 kg at 305 days and by 15% in cows who produce more than 10,000 kg. Over a period of 10 years in the dairy herds studied, the average milk production increased from 6800 kg in 1990 to 8800 kg in 2001, while CR1 decreased from 44% to 39%. Nutrition influences the reproductive endocrinology of the cow. High proportions of degradable protein in the diet, and lower feed intake (as a proportion of the body weight) are nutrition factors related to lower fertility. Any deficiencies are difficult to separate from the animal’s production level: high-producing cows are very much susceptible to Negative Energy Balance (NEB) after calving at the very moment they should normally initiate a phase of reproductive cycling. In suckling and low-milk yield cows, this period is followed by a resumption of gonadotrophic and ovarian activity and, most often, normal fertility. High-producing dairy cows, however, have often extended periods of anovulatory anestrus, as a consequence of the inadequate hormonal balance that the catabolic NEB causes (low blood levels of LH, insulin and IGF-I), resulting in impaired follicle development, estrous signs, LH surge and ovulation. Moreover, high-producing cows in NEB experience a delayed onset of postpartum ovarian activity and reduced Progesterone levels, which is caused by a lack of ovarian luteinized tissue or a higher rate of metabolism of the hormone by increased feed intake.
3. Primary, non-infectious, causes for reproductive failure in high-producing dairy cattle –
High producing cows with hormonal imbalances have shorter estrous cycles and depict fewer estrus signs than expected (Figure 1), owing to sub-optimal estradiol levels. Hormonal imbalances, as well as genetic factors are related to cystic ovarian disease in high milk yield cows. Oocyte quality, built upon a total maturation time in the ovary of around 3 months, is very sensitive to negative influences such as nutritional deficiencies or over-conditioning. Accumulation of NEFA derived from the adipose tissue during NEB in the follicle fluid constrains the proliferation and health of the granulosa cells and thus jeopardizes oocyte development. Extension of the pre-ovulatory phase, i.e. delayed ovulation, due to suprabasal P4-levels causes ageing processes in the oocyte and compromises fertility, leading to repeat breeding by fertilization failure. After fertilization, an embryo is formed which develops in the oviduct during the first 3 – 4 days before it enters the uterus. The embryonic period lasts up to day 42 after fertilization and involves a series of critical periods, of which one comprises the first three weeks of development (“early embryonic death”), accounting for ~20% of the total losses. From this moment up to day 42, losses are termed “late embryonic death”. While fertilization failure and early embryonic death relate to a low genetic index of the female, up to 25% of late embryonic deaths have been seen in cows with genetic potential for a high milk yield but mainly related to milk yield rather than to their genetic index. Some of the early embryo losses might result from a malfunctional cytoplasm which impairs further development of the fertilized oocyte, a situation seen in over-conditioned repeat breeders. Cytokines can adversely affect uterine function and indirectly cause early embryonic death in relation to mastitis during early lactation.
4. Influence of artificial control of the estrus cycle –
The increasingly common use of protocols for the hormonal control of estrus has so far produced varying results, ranging from negative effects (Donovan et al., 2003; Morel et al., 1991), to no effect (Xu et al., 1998) to positive effects on dairy cow fertility (McIntosh et al., 1984). However, researchers have noted that fertility in these cases is not affected when inseminations are made upon observed estrus. Fixed-time insemination without prior estrus detection is an approach that has gained in popularity, but it is generally recognized that it can result in decreased conception rates at first AI (Lucy, 2001). According to one study, the use of prostaglandins (with or without a synchronization protocol) for estrus induction is associated with a decrease of approximately 3% conception rates.
5. Progesterone concentrations –
Circulating concentrations of progesterone are higher in nulliparous heifers as compared to lactating cows (Sartori et al., 2004; Wolfenson et al., 2004; Rizos et al., 2010). In part, this physiological difference reflects increased post-prandial metabolism of progesterone by the liver (Sangsritavong et al., 2002; Vasconcelos et al., 2003). The reduction in circulating progesterone concentrations is likely to be one cause of reduced fertility in lactating dairy cows. Cows with higher progesterone concentrations after insemination have been reported to be more fertile (Stronge et al., 2005; Demetrio et al., 2007).
6. Decrease in fertility due to disease –
Studies have shown that disease, whether or not it is associated with the reproductive system, has a greater impact on fertility than milk production (Eicher and coll., 1996; Gröhn and Rajala-Schultz, 2000; Loeffler and coll., 1999). Data analysis has shown that metritis, dystocia, lameness, mastitis, and retained placenta all have a negative effect on conception rate, decreasing it at respective rates of: 8.0%, 6.0%, 4.3%, 2.8% and 2.5% respectively (Bouchard and Tremblay, 2003).
Strategies to ensure good fertility in high producing dairy cattle with pros and cons———–
As already mentioned, infertility in dairy cattle is multifaceted problem; therefore it requires a multi disciplinary approach. However, not all solutions intended for amelioration of the problem are longlasting, feasible or acceptable. Some measures can be applied rather immediately while others require further research and long-term strategies. Emphasis is needed on the relation between management and genetic gains, considering that many of the current problems with dairy cow fertility are a logical consequence of the low profit margins of the dairy sector, which impinges for high milk yields. With a global trend of strict cost controls, increased herd sizes, and changing farming systems, there is an unfortunate association with shortages of skilled labour and less time to look for physiological signals in the herd, the basis for good management. Moreover, we should recognize our limited ability to prevent and treat diseases, to appropriately manage, feed and select dairy cows with desirable reproductive traits.
1) Manipulation of the estrous cycle through management of floor and staff-
From a veterinary medicine perspective, manipulation of the estrous cycle and the control of ovulation appear as a good short-term strategy. Application of methods to control the development of follicle growth, the promotion of ovulation in anoestrus cows, the regression of the corpus luteum in cyclic cows and the synchronization of estrus and ovulation at the end of treatment, before AI (on spontaneous or expected estrus) or mating should be thoroughly studied. However, we should try to detect natural heat in cows in normal cycle and natural mating should be preferred if possible. Well designed cow barns, with good width and slip resistance of the flooring of passageways and holding areas support best animal well-being and allow for efficient health management, including reproduction, by promoting expression of behavioural estrus, and providing the best opportunities for estrus detection by the staff. However, detection of estrus or of health problems (e.g. lameness) is often constrained by the shortage of skilled and experienced personnel to spend enough time with the animals.
2)Transition management (fresh cow care)–
Use of diets designed to improve fertility by counteracting specific points in relation to NEB has always been an attractive way to avoid the impairment of reproduction during early lactation. However, the cow is biologically driven to mobilize body fat when she is fatter than her biological target condition, which makes this strategy difficult. Several ways have been attempted to reduce the effect of NEB, namely
1) Body Condition Scoring (BCS) of cows should be 3.5-3.75 at calving, to avoid the limiting negative feedback effect of body fat on the cow´s DMI, but high-quality diets should be available for “thinner” cows.
2) The feeding of low-protein diets that reduce body-fat mobilization by provoked imbalance in the protein-to-energy ratio.
3) The change of carbohydrate source in the diet to increase dietary energy concentration (increasing starch or fat and decreasing forage content, a risky procedure because of its implications on rumen function, milk composition, nutrient partition and metabolic hormones.
4) The inhibition of milk fat synthesis with exogenous conjugated linoleic acid (CLA), thus limiting energy output in milk. Changes in diet composition can elicit large changes in insulin levels, since plasma insulin concentrations are positively related to dietary starch concentration. Therefore, attempts have been made to use exogenous propylene glycol or hyperinsulinemic diets with the purpose of “fooling” the cow into a virtual anabolic condition, increasing glucose and insulin concentrations in circulating blood. Combinations of these designed diets are obviously more attractive, because they have proven to increase pregnancy rates dramatically (from 27 to 60%), implying that cows producing ~10,000 kg would have a fertility comparable to cows producing ~6,000 kg, by increasing insulin status immediately postpartum, and then reducing insulin status during the mating period.
3) Managing dry period –
Shortening or eliminating the dry period has been postulated as a suitable way to quickly enhance fertility in dairy cows. This management can increase dry matter intake during the transition period, decrease milk energy output, or both. By increasing the energy status of dairy cows, there is an indirect increase in reproductive efficiency. However, such practice does not apply in general as it may have negative effects on udder health and total milk yield, and should be considered on a herd to herd basis. For involution of udder and mammary glands, minimum 60 days dry period must be provided to especially to high producing cows.
4) Extended lactation and differential milking –
Most veterinary attention in dairy cattle is required from one week before to 10 weeks after calving (important transition period), confirming that calving is a welfare risk. Moreover, it is important to avoid the impact of NEB on the resumption of reproductive function. For these reasons, voluntarily delaying the 1st postpartum AI, and attempting to have the cow calving at a calving interval of may be 18 months or so, leads to
(a) the cow prolonging its lactation (socalled “persistent” lactation),
(b) no need to look for estrus during the milk peak at early lactation, and
(c) with AI done later during lactation, the cow having a better chance of getting pregnant. Increasing milking frequency by the use voluntary milking (using robotics) promotes extended lactation, but leads to a delay in the appearance of ovulatory estrus. Moreover, using extended calving intervals means fewer calves are born per cow, persistent lactation can lead to udder health problems in cows with high somatic counts and milk production can only be reasonably maintained by compensatory feeding during the declining phase. To be economically acceptable for the farmer, the milk yield has to be maintained over time and thus requires proper management. An alternative strategy is to flatten the peak of the milk curve by employing once daily milking in early lactation (but risking udder problem). Such practice promotes earlier resumption of ovarian cyclicity by increasing nutritional status, avoiding the impact of NEB and, further, the cow can maintain BCS throughout lactation.
5) Use of high fertility Bulls –
Use of AI with semen from sires with proven high-fertility is probably the most obvious and simple recommendation. However, in order to prolong the term of this strategy from short to medium, the breeding selection must be appropriate, i.e., including fertility traits with a certain weight in order to warrant that the improvement of reproductive performance is selected while still maintaining enough yearly increase in milk yield, thus warranting the profitability of dairy production in a longer perspective. 6) Crossbreeding – Use of semen from other breeds where the decline in fertility is not a severe problem is also a medium term alternative to decrease fertility deterioration, although it might not be the best long term strategy. This strategy may also be used to combat inbreeding in herds where the problem is large. In particular, the development of multiple lines with similar capacity for milk production is attractive, based on the assumption that crossbreeding could be used to exploit benefits of heterosis. However, we should always bear in mind that cross-breeding is not per se genetic improvement and that genetic selection is still needed within the breeds used.
Conclusion
The nutrition and general management of dairy cows have both changed considerably in the past years. Changes have generally been made by trying to adapt the cow to nutrition and management without considering the long term consequences on the basic reproductive physiology of the animal. Since reproductive parameters have low heritability, the application of new reproductive techniques requires an adapted reproductive health program that deserves further exploration to prevent the Udecreasing fertility in cows.
