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Environmental Stress Effects on Bovine Reproduction
FEMALE BOVINE INFERTILITY
0749-0720/93 $0.00 + .20
ENVIRONMENTAL STRESS EFFECTS ON BOVINE REPRODUCTION c.
N. Lee, PhD
All living things are dependent on their environment, given that their ability to adapt to the changes in climatic conditions and to utilize the resources available are crucial to their survival. Those that fail to integrate into the bio-ecosystem become weak, fall sick and become prey to others. The process of adaptation results in evolution of both phenotypic and physiologic factors. In today's modern livestock production units, the process of evolution within a breed or species is accelerated by human intervention. Knowledge of genetics, physiology, nutrition, diseases, and management provides Homo sapiens with tools to select desirable characteristics or production traits in domestic livestock. In addition, our knowledge of physical sciences allows us to control the environment in which these animals are housed. This is particularly true where weather conditions are harsh. Although the initial intent of animal housing was to provide humans with a more comfortable environment in which to work, in recent years, more consideration has been given to animal comfort and welfare. Severe weather conditions or fluctuations add stress to livestock, affecting both production and reproduction. DEFINITION OF STRESS
Individuals involved in animal husbandry commonly use the word stress to indicate environmental factors that alter the normal state of From the Department of Animal Sciences, University of Hawaii-Manoa, Honolulu, Hawaii
VETERINARY CLINICS OF NORTH AMERICA: FOOD ANIMAL PRACTICE VOLUME 9 • NUMBER 2 • JULY 1993
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well-being of the animal. Such factors are not limited to climatic elements but include food and water deprivation, diseases, external parasites, restraint, transportation, and social pressure-e.g., pecking order. The word stress was derived from the word distress following the slurring of the first syllable. Wunder67 has questioned the limited scope of the word when used to define the restoration of normal physiologic well-being. Lee44 suggested that the word should not depart from its original concept used in physical sciences. He proposed that stress denotes "the magnitude of forces external to the bodily system which tend to displace that system from its resting or ground state." Stotfi7 further suggested that stress should include all forces or stimuli, internal and external, that can induce changes in the animal to allow it to adapt to its environment. This change can also result in economic traits that can benefit humans-e.g., improved reproduction, production, and so on. Hence, in most cases, stress measurement takes a "cause and effect" approach. The long-term implications of stress on the animal are difficult to measure because changes at the cellular level are more subtle. Nevertheless, they can be of economic importance to a livestock producer. NUTRITIONAL STRESS AFFECTS REPRODUCTION
The postpartum cow has conflicting biologic needs-demands for maintenance, lactation, resumption of estrous cycle, embryonic development, and, in first-calved heifers, growth. 54 Lactating beef cows that are underfed have lower plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH).59 Lower frequency of LH pulses and inhibition of LH release have been observed following calf removal in cows under chronic malnutrition. 66 The lower LH and FSH levels are not caused by a decrease in sensitivity of the pituitary, but rather a decrease in the gonadotropin pulses. 59 The decrease in gonadotropin-releasing hormone pulses may lead to delay in folliculogenesis in the postpartum period and subsequent increases in the time to first postpartum estrus. 17, 19 Similar findings have been reported in rats 10 and sows 4 on restricted energy diets. In sows, a lower LH surge was observed at estrus. If the state of chronic malnutrition is extended over a long period, cessation of estrous cycle occurs. 4 ,9 In dairy cows, nutrient utilization for milk production has top priority. Cows lose body weight in the initial stages of lactation and have to mobilize body reserves to meet lactation demands. Butler and Smith13 summarized data that showed a 16% decline in conception rates during a period (1951-1973) when milk production increased 33%. This decline in conception has stabilized even though increases in milk production continued. 55 Conception rates for heifers had remained the same over the years, suggesting that this decline is not attributable to genetic factors, but rather to competing demands for nutrients for maintenance and lactation versus reproduction.
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A negative relationship has been documented between energy balance and number of days to ovulation in dairy animals. 14 Regression equations relating energy levels and body weight changes predict postpartum intervals of fewer than 50 days for multiparous cows and 50 to 60 days for primiparous cows. 19, 65 Several reviews suggest that prepartum nutrition is just as important as postpartum nutrition in determining the resumption of estrous cyclicity in cattle. 19, 21, 50 Although there are conflicting reports l8, 26, 47, 56 on progesterone concentrations under nutritional stress, it is generally accepted that corpora lutea from nutritional stressed animals are lighter in weight. 7, 26,31,33 Boice l l showed that 14% of postpartum dairy cows did not have sufficient progesterone to maintain pregnancy. Low progesterone concentrations have also been reported in repeat breeder COWS. 12, 22 Higher progesterone levels in previous estrous cycles24 or in the early luteal phase have been reported to enhance conception rates. 40, 51 Recent studies from our laboratory demonstrate that nutritional stress results in lower weights of 30-day-old embryos. Although luteal function was maintained, the chemical constituents of allantoic fluids indicated that embryos from malnourished cows were degenerating. 41 Most embryos became an amorphous red residue in the amniotic sac by day 37 to 40.
Dietary Proteins and Fertility
Dietary composition also plays an important role in reproduction. In one study, diets inadequate in protein resulted in 42% lower conception rates;52 others report detrimental effects of excessive protein levels. 23,37 When urea nitrogen levels in female reproductive secretions exceed 40 mgllOO mL, cows do not conceive. 15 The source of protein also may affect reproduction, given that several studies demonstrated negative effects of gossypol (present in cotton products) on embryo development,69 steroidogenesis of luteal cells,27 and spermatogenesis. 5 For further details concerning nutritional effects on reproduction, examine the reviews listed in Table 1. Table 1. A SELECTION OF JOURNAL ARTICLES ON NUTRITIONAL AND OTHER PHYSIOLOGIC EFFECTS ON REPRODUCTION
Species Dairy Dairy Dairy Dairy Beef Beef Beef Beef
Authors
Year
Source
Butler et al Ducker et al Butler et al Ferguson, Chalupa Dunn, Kaltenbach Hanzen Randel Short et al
1981 1985 1989 1989 1980 1986 1990 1990
J Anim Sci 53:742 Anim Prod 41 :1 J Dairy Sci 72:767 J Dairy Sci 72:746 J Anim Sci 51 :29 Reprod Nutr Dev 26:219 J Anim Sci 68:853 J Anim Sci 68:799
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ENDOCRINOLOGIC CHANGES UNDER HEAT STRESS CONDITIONS
High ambient temperatures alter reproductive hormone profiles in cows. Several studies have shown that cows under heat stress conditions secrete higher levels of progesterone. 20, 29, 43 The adrenal gland has been suggested as a source of this progesterone. This level of progesterone (>0.7 ng/mL) may inhibit the LH surge of estrus (Fig. 1). It has been demonstrated that exogenous progesterone has the ability to inhibit the LH surge of estrus 39 and prevent ovulation. 53 Luteinizing hormone patterns following prolonged heat stress have also been shown to be altered. Cows in pens with no shade demonstrate a lack of synchronous secretion of LH at estrus compared with cows in shaded pens following synchronization with prostaglandins (Fig. 2). Madan and Johnson45 showed decreased LH peaks at estrus, although it is unclear whether the lower peaks would contribute to lower pregnancy rates. The intensity of estrous behavior decreases under heat stress conditions. 25 Shortened duration of estrus and even anestrus have been reported. 25, 43 This alteration in estrous behavior prompted Badinga et al 6 and Hall et apo to suggest breeding cows when they are in standing heat; both studies reported higher conception rates. Cortisol, prolactin, and thyroxine have been reported to be altered by heat stress conditions, although their direct negative effects on reproduction under such circumstances have yet to be firmly established. Although cortisol levels usually rise in acute response to heat, 3 Progesterone (ng/ml) 2.5r---------------------------------------------------~
2
--*-
no shade-no LH surge
-
no shade-wi LH surge
~ shade-wi LH surge
1.5
1
0.5 o~------~--------~------~------~~------~------~
1
2
345
6
7
Sample numbers Figure 1. Plasma progesterone (ng/mL) of cows under shade and no shade environment in the subtropics. Sampling began at 3:00 p.m. at 8-hour intervals. Patterns differ (P < 0.01). (From Lee CN, Vincent DL, Weems CW, et al: Endocrine profiles of lactating cows under shade and no shade environments in the subtropics. HITAHR Res Series #70,1994, in press; with permission.)
ENVIRONMENTAL STRESS EFFECTS ON BOVINE REPRODUCTION
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LH (ng/ml)
18~--------------------------------------------~
16 14 12 10
8 6 4 2 O~~~~~~~~~~~~~~~-;~~~~~~~~~
3PM
11PM
7AM
3PM
11PM
7AM
3PM
TIME Figure 2. Plasma luteinizing hormone (LH) for cows in shaded pens compared with pens with no shade. Patterns differ (P < 0.01). (From Lee CN, Vincent DL, Weems CW, et al: Endocrine profiles of lactating cows under shade and no shade environments in the subtropics. HITAHR Res Series #70, 1994, in press; with permission.)
they are lower in cows in chronic heat stress environments. 2 Thyroxine and triiodothyronine decrease under heat stress conditions, resulting in lower heat production, thereby enabling the animal to adjust to greater environmental heat loads. 46, 68 Subsequently, feed intake will be lower,46 also leading to a reduction in heat production, lower milk production, and lower reproduction due to energy and essential nutrients deprivation.
Conception Rate Under Heat Stress Environment
The thermal neutral or comfort zone for cattle varies with breed and climatic elements of wind, solar radiation, temperature, and humidity. 35, 36 This zone usually is expressed as a temperature-humidity index (THI),l with 72 being upper critical level for most temperate cattle. The severity of ambient temperature's effects on fertility was demonstrated in a study by Dunlap and Vincent. 2o Conception rates for cows exposed to 21°C and 32°C for 72 hours were 56% versus 0%, respectively. Seasonal declines in conception rates in hot climates are well documented. 34, 49, 58 When the THI increases from 68 to 78, conception rates decrease from 66% to 35%.33 The THI two days prior to breeding has a significant effect on conception rates. Work in Florida suggests that increases in vaginal temperatures by 0.5°C on the day of or the day after breeding are associated with declines in conception
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rates. When rectal temperatures in cows increase 1°C, pregnancy rates drop 16%.60 It is common for cows in hot, humid regions to have rectal temperatures above 39.5°C during the day.43 Summer temperatures are unlikely to reduce pregnancy rates in virgin heifers (Table 2). This is in agreement with earlier studies. 6,28 Pregnancy rates of heifers decline when temperatures exceed 35°C, however.6 In subtropical climates like Hawaii, we observe higher pregnancy rates when cows are bred in the late afternoon, leading into the cooler time of the day (see Table 2). Solar radiation load also has been shown to have a curvilinear effect on reproduction. As the radiation load increases from 300 to 800 Langleys/day, conception rates decrease from 39.5% to 26%.28 Lee et al 43 showed that even when the THI for shade and no shade environments was the same, cows in the no shade pens had significantly higher rectal temperatures during the day. They attribute this increase in rectal temperatures to solar radiation load on the cows. Age, breed, and number of lactations are some other factors contributing to lower fertility in hot climates. Jerseys have higher fertility rates than Brown Swiss and Holsteins6, 28 in the subtropics. Nulliparous heifers have the highest fertility rates (>47%), followed by cows with fewer than four lactations (43%), then older cows (32%).28 Heat Stress and Loss of Embryos
The poorer conception rates under heat stress usually are attributed to reproductive failure in the female. The number of normal embryos are 23% lower and the number of retarded embryos are 25% higher in heat stressed heifers than in controls.48 Similar numbers of ova are unfertilized. Ulberg and Burfening60 showed that the developmental stages of fertilized egg cleavage are hampered by high temperatures but fertilization rate is not. Their studies also show that sperm cells collected from males exposed to high temperatures are just as effective in fertilizing ova as those of control males but the embryos fail to develop beyond the implantation stage. In another experiment with Table 2. CONCEPTION RATES OF COWS AND HEIFERS IN SUBTROPICAL CLIMATES (HAWAII) DURING HOT AND COOL MONTHS AND COMPARING MORNING VERSUS LATE DAY BREEDING* Hot versus Cool Months Cows Commercial dairies Research herd Research herd heifers AM
versus
*N
PM
N
Hot
N
Cool
P value
4592 230 110
34.2% 50.6% 63.7%
3297 278 96
20.7% 66.3% 70.8%
<.01 <.01 >.05
Breeding
N
AM
N
PM
P value
7116
30.9%
503
38.8%
<.05
= number
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rabbits, they provide evidence suggesting that there are differences in fertility of the bucks under heat stress. Further research is needed to determine whether this phenomenon exists in bulls. Differences in ion concentrations in amniotic and allantoic fluids from 30-day-old embryos from cows subjected to heat stress conditions from days 17 to 30 postbreeding suggest that high temperatures are detrimental to embryos even following maternal recognition of pregnancy.42 Heat stressed gilts reduce the amount of conceptus tissue and alter peripheral estradiol concentrations;64 heat stressed ewes reduce progesterone and prolactin production, 8 resulting in placental stunting as they attempt to cope with the demands of the environment. COLD STRESS
Little is known about the effects of cold environments on reproductive processes. Serum thyroxine and triiodothyronine concentrations increase significantly when animals are in the lower critical temperature zone. 63 This results in increased rumen motility and rate of passage of digesta, leading to an increase in dry matter intake. The higher intake is reflective of the need of the animal to produce more energy for warmth. Under severe cold conditions, therefore, pregnant beef cows on pasture without supplementation may lose substantial body weight, resulting in weaker calves. 38 Dairy cows normally are provided with some form of shelter during the winter months. Although the objective of providing shelter is to provide a comfortable environment for dairy producers, these shelters are sufficient in providing warmth and comfort to the cows. The animals therefore seldom are exposed to environmental zones below the critical limit that will have drastic effects on reproduction. MANAGEMENT ALTERNATIVES TO ALLEVIATE STRESS
Balancing rations to meet the animal's demands is one of the key elements for a successful operation. One must have an understanding of the nutrient availability of feed ingredients as well as the animal's needs under different environments. A cow under heat stress conditions has depressed dry matter intake at the same time it is losing large quantities of sodium, potassium, and chloride because of panting, sweating, and salivation. Rumen pH also may decrease. The supplementation of buffers-e.g., sodium bicarbonate or potassium-may help restore appetite and rumen pH, and may even result in higher milk production. 16, 62 Simple shade shelters, fans, and misters can cool cows readily and result in higher milk production32 and reproduction. 43 A hundred percent of Holstein cows under shade exhibited standing estrus but
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only 27.5% in pens with no shade demonstrated mounting behavior.43 The endocrine profiles from cows housed under shade in the subtropics are similar to those in temperate regions. In almost all cases, these investments 43 pay for themselves rapidly.
SUMMARY
Environmental stress is not limited to climatic factors but extends to nutrition, housing, and any stimuli that demand a response from the animal to adapt to new circumstances. Low energy and low or excessive protein levels in the diet are detrimental to reproduction. Likewise, high ambient temperatures and humidity alter the intricate balance of endocrine profiles, leading to lower intensity of estrous behavior, anestrus, embryonic death, and subsequent infertility. Most of these stress factors can be managed with modern technologies to achieve maximum production. Further research in vitamins and minerals under heat stress may add to the knowledge of efficient livestock production.
References 1. A Guide to Environmental Research on Animals. Washington DC, National Academy of Sciences. 1971, p 77 2. Abilay TA, Johnson HD, Mada M: Influence of environmental heat on peripheral plasma progesterone and cortisol during the bovine estrus cycle. J Dairy Sci 58:1836, 1974 3. Abilay TA, Mitra R, Johnson HD: Plasma cortisol and total progestin levels in Holstein steers during acute exposure to high environmental temperature (42°C) conditions. J Anim Sci 41:113, 1975 4. Armstrong J, Britt JH: Nutritionally induced anestrus in gilts: metabolic and endocrine changes associated with cessation and resumption of estrous cycles. J Anim Sci 65:508, 1987 5. Arshami J, Ruttle JL: Effects of diets containing gossypol on spermatogenic tissues of young bulls. Theriogenology 30:507, 1988 6. Badinga L, Collier RJ, Thatcher WW, et al: Effects of climatic and management factors on conception rate of dairy cattle in subtropical environment. J Dairy Sci 68:78, 1985 7. Beal WE, Short RE, Staigmiller RB, et al: Influence of dietary energy intake on bovine pituitary and luteal function. J Anim Sci 46:181, 1978 8. Bell AW, McBride BW, Slepetis R, et al: Chronic heat stress and prenatal development in sheep: 1. Conceptus growth and maternal plasma hormones and metabolites. J Anim Sci 67:3289, 1989 9. Bond J, Wiltbank IN, Cook AC: Cessation of estrus and ovarian activity in a group of beef heifers on extremely low energy and protein. J Anim Sci 17:1211, 1958 10. Bronson FH: Food-restricted, prepubertal female rats: rapid recovery of luteinizing hormone pulsing with excess food, and full recovery of pubertal development with gonadotropin-releasing hormone. Endocrinology 118:2483, 1986 11. Boice ML: The relationship between estrous behavior, ovarian activity and milk progesterone in postpartum Holstein cows. MSc Thesis. Champaign-Urbana, University of Illinois, 1979 12. Bulman DC, Lamming GE: Milk progesterone levels in relation to conception, repeat breeding and factors influencing acyclicity in dairy cows. J Reprod Ferti154:447, 1978
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l3. Butler WR, Smith RD: Interrelationships between energy balance and postpartum reproductive function in dairy cattle. J Dairy Sci 72:767, 1989 14. Butler WR, Everett RW, Coppock CE: The relationship between energy balance, milk production and ovulation in postpartum Holstein cows. J Anim Sci 53:742, 1981 15. Carroll DJ, Barton BA, Anderson, GW, et al: Influence of protein intake and feeding strategy on reproductive performance of dairy cows. J Dairy Sci 71:3470, 1988 16. Coppock CE, Grant PA, Portzer SJ, et al: Lactating dairy cow responses to dietary sodium, chloride and bicarbonate during hot weather. J Dairy Sci 65:566, 1982 17. Corah LR, Dunn TG, Kaltenbalch CC: Influence of prepartum nutrition on the reproductive performance of beef females and the performance of their progeny. J Anim Sci 41:819, 1975 18. Donaldson LE, Basset JM, Thorburn GD: Peripheral plasma progesterone concentration of cows during puberty, oestrous cycles, pregnancy and lactation and the effects of undernutrition or exogenous oxytocin on progesterone concentration. J Endocrinol 48:599, 1970 19. Dunn TG, Kaltenbach CC: Nutrition and the postpartum interval of the ewe, sow and cow. J Anim Sci 51:29, 1980 20. Dunlap SE, Vincent CK: Influence of postbreeding thermal stress on conception rate in beef cattle. J Anim Sci 32:1216, 1971 21. Dzuik PI, Bellows RA: Management of reproduction of beef cattle, sheep and pigs. J Anim Sci 57:355, 1983 22. Erb RE, Garverick HA, Randel RD: Profiles of reproductive hormones associated with fertile and nonfertile inseminations of dairy cows. Theriogenology 5:227, 1976 23. Folman Y, Neumark H, Kaim M, et al: Performance, rumen and blood metabolites in high yielding cows fed various protein percents and protected soybean. J Dairy Sci 64:759, 1981 24. Fonseca FA, Britt JH, McDaniel BT, et al: Reproductive traits of Holsteins and Jerseys: Effects of age, milk yield, and clinical abnormalities on involution of cervix and uterus, ovulation estrous cycles, detection of estrus, conception rate and days open. J Dairy Sci 66:1128, 1983 25. Gangwar PC, Branton C, Evans DL: Reproductive and physiological responses of Holstein heifers to controlled and natural climatic conditions. J Dairy Sci 48:222, 1965 26. Gombe S, Hansel W: Plasma luteinizing hormone and progesterone levels in heifers on restricted energy intake. J Anim Sci 37:728, 1973 27. Gu Y, Rikihisa Y, Lin YC: Inhibitory effect of gossypol (GP) on steroid metabolic pathways in cultured bovine luteal cells (BLC). BioI Reprod 40:59, 1989 28. Gwazdauskas FC, Wilcox CJ, Thatcher WW: Environmental and management factors affecting conception rate in a subtropical climate. J Dairy Sci 58:88, 1975 29. Gwazdauskas FC, Thatcher WW, Wilcox CJ: Physiological, environmental, and hormonal factors at insemination which may affect conception. J Dairy Sci 56:873, 1973 30. Hall JG, Branton C, Stone EJ: Estrus, estrous cycles, ovulation time, time of service and fertility of dairy cattle in Louisiana. J Dairy Sci 42:1086, 1959 31. Hill JR, Lamond SR, Henricks DM, et al: The effect of undernutrition on ovarian function and fertility in beef heifers. BioI Reprod 2:78, 1970 32. Igono MO, Johnson HD, Steevens BJ, et al: Physiological, productive and economic benefits of shade, spray and fan system versus shade for Holstein cows during summer heat. J Dairy Sci 70:1069, 1987 33. Imakawa K, Kittock RJ, Kinder JE: The influence of dietary energy intake on progesterone concentrations in beef heifers. J Anim Sci 56:454, 1983 34. Ingraham RH, Stanley RW, Wagner WC: Relationship of temperature and humidity to conception rate of Holstein cows in Hawaii. J Dairy Sci 59:2086, 1976 35. Johnson HD: Climatic effects on physiology and productivity of cattle. In Shaw RH (ed): Ground Level Climatology. Baltimore, Horn-Shafer, 1967, p 189 36. Johnson HD: Bioclimate effects on growth, reproduction and milk production. In Bioclimatology and the Adaption of Livestock. Amsterdam, Elsevier, 1987, p 35 37. Jordon ER, Swanson LV: Effect of crude protein on reproductive efficiency, serum total protein and albumin in the high-producing dairy cow. J Dairy Sci 62:58, 1979 38. Jordan WA, Lister EE, Rowlands GJ: Effect of planes of nutrition on wintering pregnant beef cows. Can J Anim Sci 48:145, 1968
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39. Lee CN, Cook DL, Parfet JR, et al: Induction of persistent ovarian follicular structures following administration of progesterone near the onset of estrus in cattle. J Dairy Sci 71:3505, 1988 40. Lee CN, Critser JK, Ax RL: Changes of luteinizing hormone and progesterone for dairy cows after gonadotropin-releasing hormone at first postpartum breeding. J Dairy Sci 68:1463, 1985 41. Lee CN, Vincent DL, Nusser KD, et al: Chemical analyses of allantoic fluid from bovine embryos recovered from dams subjected to nutritional stress. BioI Reprod 40:65, 1989 42. Lee CN, Vincent DL, Weems CW, et al: Chemical constituents of allantoic and amniotic fluid of 30 days old bovine embryos under shade or no shade environment. BioI Reprod 44:173, 1991 43. Lee CN, Vincent DL, Weems CW, et al: Endocrine profiles of lactating cows under shade and no shade environments in the subtropics. HITAHR Res Series #70, 1994, in press 44. Lee DHR: Climatic stress indices for domestic animals. Int J Biometeorol 9:29, 1965 45. Madan ML, Johnson HD: Environmental heat effects on bovine luteinizing hormone. J Dairy Sci 56:1420, 1973 46. Magdub A, Johnson HD, Belyea RL: Effect of environmental heat and dietary fiber on thyroid physiology of lactating cows. J Dairy Sci 65:2323, 1982 47. McCann JP, Hansel W: Relationship between insulin and glucose metabolism and pituitary ovarian function in fasted heifers. BioI Reprod 34:630, 1986 48. Putney DJ, Drost M, Thatcher WW: Embryonic development in dairy cattle exposed to elevated ambient temperatures between days 1 to 7 post insemination. BioI Reprod 34:100, 1986 49. Rabeie HM: Effect of Missouri and Libyan seasonal climate on the reproductive performance of Holstein dairy cattle. MS Thesis. Columbia, MO, University of Missouri, 1983 50. Randel RD: Nutrition and postpartum rebreeding in cattle. J Anim Sci 68:853, 1990 51. Remsen LG, Roussel JD, Karihaloo AK: Pregnancy rates relating to plasma progesterone levels in recipient heifers at day of transfer. Theriogenology 18:365, 1982 52. Sasser RG, William RJ, Bull RC, et al: Postpartum reproductive performance in crude protein restricted beef cows: return to estrus and conception. J Anim Sci 66:3033, 1989 53. Sirois J, Fortune JE: Lengthening the bovine estrous cycle with low levels of exogenous progesterone: A model for studying ovarian follicular dominance. Endocrinology 127:916, 1990 54. Smidt D, Farries E: The impact of lactational performance on postpartum fertility in dairy cows. In Karg H, Schallenberger E (eds): Factors Influencing Fertility in the Postpartum Cow. Current topics in veterinary medicine and animal science. The Hague, Martinus Nijhoff, 20:358, 1982 55. Smith TR: Dairy herd profile summary and analysis. Cornell Univ Anim Sci Mimeo Ser 90:27, 1986 56. Spitzer JC, Niswender GD, Seider GE, et al: Fertilization and blood levels of progesterone and luteinizing hormone in beef heifers on a restricted energy diet. J Anim Sci 46:1071, 1978 57. Stott GH: What is animal stress and how is it measured. J Anim Sci 52:151, 1981 58. Stott GH, Williams RJ: Causes of low breeding efficiency in dairy cattle associated with seasonal high temperatures. J Dairy Sci 45:1369, 1962 59. Terqui M, Chupin D, Gauther D, et al: Influence of management and nutrition on postpartum endocrine function and ovarian activity in cows. In Karg JH, Schallenberger E (eds): Factors influencing fertility in the postpartum cow. Current topics in veterinary medicine and animal science. The Hague, Martinus Nijhoff, 20:384, 1982 60. Ulberg LC, Burfening PJ: Embryo death resulting from adverse environment on spermatozoa or ova. J Anim Sci 26:571, 1967 61. Vincent DL, Nusser KD, Carpenter JR, et al: Nutritional stress alters corpus luteum function during early pregnancy in the bovine. BioI Reprod 40:60, 1989 62. West JW, Mullinix BG, Sandifer TG: Changing dietary electrolyte balance for dairy cows in cool and hot environments. J Dairy Sci 74:1662, 1991
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63. Westra R, Christopherson RJ: Effects of cold on digestibility, retention time of digesta, reticulum motility and thyroid hormones in sheep. Can J Anim Sci 56:699, 1976 64. Wettemann RP, Bazer FW, Thatcher WW, et al: Conceptus development, uterine response, blood gases and endocrine function of gilts exposed to increased ambient temperature during early pregnancy. Theriogenology 30:57, 1988 65. Wettemann RP, Lusby KS, Turman EJ: Relationship between changes in prepartum weight and condition and reproductive performance of range cows. Oklahoma Agric Exp Sta 112:12, 1982 66. Whaisnant CS, Kiser TE, Thompson FN, et al: Effect of nutrition on the LH response to calf removal and GnRH. Theriogenology 24:565, 1985 67. Wunder CC: Life in Space: An Introduction to Space Biology. Philadelphia, FA Davis, 1966 68. Yousef MK, Kible HH, Johnson HD: Thyroid activity and heat production in cattle following sudden ambient temperature changes. J Anim Sci 26:142, 1967 69. Zirkle SM, Lin YC, Gwazdauskas FC, et al: Effects of gossypol on bovine embryo development during the preimplantation period. Theriogenology 30:575, 1988
Address reprint requests to C. N. Lee, PhD World-Wide Sires, Inc 16032 South 10th Avenue Hanford, CA 93230
0749-0720/93 $0.00 + .20
ENVIRONMENTAL STRESS EFFECTS ON BOVINE REPRODUCTION c.
N. Lee, PhD
All living things are dependent on their environment, given that their ability to adapt to the changes in climatic conditions and to utilize the resources available are crucial to their survival. Those that fail to integrate into the bio-ecosystem become weak, fall sick and become prey to others. The process of adaptation results in evolution of both phenotypic and physiologic factors. In today's modern livestock production units, the process of evolution within a breed or species is accelerated by human intervention. Knowledge of genetics, physiology, nutrition, diseases, and management provides Homo sapiens with tools to select desirable characteristics or production traits in domestic livestock. In addition, our knowledge of physical sciences allows us to control the environment in which these animals are housed. This is particularly true where weather conditions are harsh. Although the initial intent of animal housing was to provide humans with a more comfortable environment in which to work, in recent years, more consideration has been given to animal comfort and welfare. Severe weather conditions or fluctuations add stress to livestock, affecting both production and reproduction. DEFINITION OF STRESS
Individuals involved in animal husbandry commonly use the word stress to indicate environmental factors that alter the normal state of From the Department of Animal Sciences, University of Hawaii-Manoa, Honolulu, Hawaii
VETERINARY CLINICS OF NORTH AMERICA: FOOD ANIMAL PRACTICE VOLUME 9 • NUMBER 2 • JULY 1993
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well-being of the animal. Such factors are not limited to climatic elements but include food and water deprivation, diseases, external parasites, restraint, transportation, and social pressure-e.g., pecking order. The word stress was derived from the word distress following the slurring of the first syllable. Wunder67 has questioned the limited scope of the word when used to define the restoration of normal physiologic well-being. Lee44 suggested that the word should not depart from its original concept used in physical sciences. He proposed that stress denotes "the magnitude of forces external to the bodily system which tend to displace that system from its resting or ground state." Stotfi7 further suggested that stress should include all forces or stimuli, internal and external, that can induce changes in the animal to allow it to adapt to its environment. This change can also result in economic traits that can benefit humans-e.g., improved reproduction, production, and so on. Hence, in most cases, stress measurement takes a "cause and effect" approach. The long-term implications of stress on the animal are difficult to measure because changes at the cellular level are more subtle. Nevertheless, they can be of economic importance to a livestock producer. NUTRITIONAL STRESS AFFECTS REPRODUCTION
The postpartum cow has conflicting biologic needs-demands for maintenance, lactation, resumption of estrous cycle, embryonic development, and, in first-calved heifers, growth. 54 Lactating beef cows that are underfed have lower plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH).59 Lower frequency of LH pulses and inhibition of LH release have been observed following calf removal in cows under chronic malnutrition. 66 The lower LH and FSH levels are not caused by a decrease in sensitivity of the pituitary, but rather a decrease in the gonadotropin pulses. 59 The decrease in gonadotropin-releasing hormone pulses may lead to delay in folliculogenesis in the postpartum period and subsequent increases in the time to first postpartum estrus. 17, 19 Similar findings have been reported in rats 10 and sows 4 on restricted energy diets. In sows, a lower LH surge was observed at estrus. If the state of chronic malnutrition is extended over a long period, cessation of estrous cycle occurs. 4 ,9 In dairy cows, nutrient utilization for milk production has top priority. Cows lose body weight in the initial stages of lactation and have to mobilize body reserves to meet lactation demands. Butler and Smith13 summarized data that showed a 16% decline in conception rates during a period (1951-1973) when milk production increased 33%. This decline in conception has stabilized even though increases in milk production continued. 55 Conception rates for heifers had remained the same over the years, suggesting that this decline is not attributable to genetic factors, but rather to competing demands for nutrients for maintenance and lactation versus reproduction.
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A negative relationship has been documented between energy balance and number of days to ovulation in dairy animals. 14 Regression equations relating energy levels and body weight changes predict postpartum intervals of fewer than 50 days for multiparous cows and 50 to 60 days for primiparous cows. 19, 65 Several reviews suggest that prepartum nutrition is just as important as postpartum nutrition in determining the resumption of estrous cyclicity in cattle. 19, 21, 50 Although there are conflicting reports l8, 26, 47, 56 on progesterone concentrations under nutritional stress, it is generally accepted that corpora lutea from nutritional stressed animals are lighter in weight. 7, 26,31,33 Boice l l showed that 14% of postpartum dairy cows did not have sufficient progesterone to maintain pregnancy. Low progesterone concentrations have also been reported in repeat breeder COWS. 12, 22 Higher progesterone levels in previous estrous cycles24 or in the early luteal phase have been reported to enhance conception rates. 40, 51 Recent studies from our laboratory demonstrate that nutritional stress results in lower weights of 30-day-old embryos. Although luteal function was maintained, the chemical constituents of allantoic fluids indicated that embryos from malnourished cows were degenerating. 41 Most embryos became an amorphous red residue in the amniotic sac by day 37 to 40.
Dietary Proteins and Fertility
Dietary composition also plays an important role in reproduction. In one study, diets inadequate in protein resulted in 42% lower conception rates;52 others report detrimental effects of excessive protein levels. 23,37 When urea nitrogen levels in female reproductive secretions exceed 40 mgllOO mL, cows do not conceive. 15 The source of protein also may affect reproduction, given that several studies demonstrated negative effects of gossypol (present in cotton products) on embryo development,69 steroidogenesis of luteal cells,27 and spermatogenesis. 5 For further details concerning nutritional effects on reproduction, examine the reviews listed in Table 1. Table 1. A SELECTION OF JOURNAL ARTICLES ON NUTRITIONAL AND OTHER PHYSIOLOGIC EFFECTS ON REPRODUCTION
Species Dairy Dairy Dairy Dairy Beef Beef Beef Beef
Authors
Year
Source
Butler et al Ducker et al Butler et al Ferguson, Chalupa Dunn, Kaltenbach Hanzen Randel Short et al
1981 1985 1989 1989 1980 1986 1990 1990
J Anim Sci 53:742 Anim Prod 41 :1 J Dairy Sci 72:767 J Dairy Sci 72:746 J Anim Sci 51 :29 Reprod Nutr Dev 26:219 J Anim Sci 68:853 J Anim Sci 68:799
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ENDOCRINOLOGIC CHANGES UNDER HEAT STRESS CONDITIONS
High ambient temperatures alter reproductive hormone profiles in cows. Several studies have shown that cows under heat stress conditions secrete higher levels of progesterone. 20, 29, 43 The adrenal gland has been suggested as a source of this progesterone. This level of progesterone (>0.7 ng/mL) may inhibit the LH surge of estrus (Fig. 1). It has been demonstrated that exogenous progesterone has the ability to inhibit the LH surge of estrus 39 and prevent ovulation. 53 Luteinizing hormone patterns following prolonged heat stress have also been shown to be altered. Cows in pens with no shade demonstrate a lack of synchronous secretion of LH at estrus compared with cows in shaded pens following synchronization with prostaglandins (Fig. 2). Madan and Johnson45 showed decreased LH peaks at estrus, although it is unclear whether the lower peaks would contribute to lower pregnancy rates. The intensity of estrous behavior decreases under heat stress conditions. 25 Shortened duration of estrus and even anestrus have been reported. 25, 43 This alteration in estrous behavior prompted Badinga et al 6 and Hall et apo to suggest breeding cows when they are in standing heat; both studies reported higher conception rates. Cortisol, prolactin, and thyroxine have been reported to be altered by heat stress conditions, although their direct negative effects on reproduction under such circumstances have yet to be firmly established. Although cortisol levels usually rise in acute response to heat, 3 Progesterone (ng/ml) 2.5r---------------------------------------------------~
2
--*-
no shade-no LH surge
-
no shade-wi LH surge
~ shade-wi LH surge
1.5
1
0.5 o~------~--------~------~------~~------~------~
1
2
345
6
7
Sample numbers Figure 1. Plasma progesterone (ng/mL) of cows under shade and no shade environment in the subtropics. Sampling began at 3:00 p.m. at 8-hour intervals. Patterns differ (P < 0.01). (From Lee CN, Vincent DL, Weems CW, et al: Endocrine profiles of lactating cows under shade and no shade environments in the subtropics. HITAHR Res Series #70,1994, in press; with permission.)
ENVIRONMENTAL STRESS EFFECTS ON BOVINE REPRODUCTION
267
LH (ng/ml)
18~--------------------------------------------~
16 14 12 10
8 6 4 2 O~~~~~~~~~~~~~~~-;~~~~~~~~~
3PM
11PM
7AM
3PM
11PM
7AM
3PM
TIME Figure 2. Plasma luteinizing hormone (LH) for cows in shaded pens compared with pens with no shade. Patterns differ (P < 0.01). (From Lee CN, Vincent DL, Weems CW, et al: Endocrine profiles of lactating cows under shade and no shade environments in the subtropics. HITAHR Res Series #70, 1994, in press; with permission.)
they are lower in cows in chronic heat stress environments. 2 Thyroxine and triiodothyronine decrease under heat stress conditions, resulting in lower heat production, thereby enabling the animal to adjust to greater environmental heat loads. 46, 68 Subsequently, feed intake will be lower,46 also leading to a reduction in heat production, lower milk production, and lower reproduction due to energy and essential nutrients deprivation.
Conception Rate Under Heat Stress Environment
The thermal neutral or comfort zone for cattle varies with breed and climatic elements of wind, solar radiation, temperature, and humidity. 35, 36 This zone usually is expressed as a temperature-humidity index (THI),l with 72 being upper critical level for most temperate cattle. The severity of ambient temperature's effects on fertility was demonstrated in a study by Dunlap and Vincent. 2o Conception rates for cows exposed to 21°C and 32°C for 72 hours were 56% versus 0%, respectively. Seasonal declines in conception rates in hot climates are well documented. 34, 49, 58 When the THI increases from 68 to 78, conception rates decrease from 66% to 35%.33 The THI two days prior to breeding has a significant effect on conception rates. Work in Florida suggests that increases in vaginal temperatures by 0.5°C on the day of or the day after breeding are associated with declines in conception
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rates. When rectal temperatures in cows increase 1°C, pregnancy rates drop 16%.60 It is common for cows in hot, humid regions to have rectal temperatures above 39.5°C during the day.43 Summer temperatures are unlikely to reduce pregnancy rates in virgin heifers (Table 2). This is in agreement with earlier studies. 6,28 Pregnancy rates of heifers decline when temperatures exceed 35°C, however.6 In subtropical climates like Hawaii, we observe higher pregnancy rates when cows are bred in the late afternoon, leading into the cooler time of the day (see Table 2). Solar radiation load also has been shown to have a curvilinear effect on reproduction. As the radiation load increases from 300 to 800 Langleys/day, conception rates decrease from 39.5% to 26%.28 Lee et al 43 showed that even when the THI for shade and no shade environments was the same, cows in the no shade pens had significantly higher rectal temperatures during the day. They attribute this increase in rectal temperatures to solar radiation load on the cows. Age, breed, and number of lactations are some other factors contributing to lower fertility in hot climates. Jerseys have higher fertility rates than Brown Swiss and Holsteins6, 28 in the subtropics. Nulliparous heifers have the highest fertility rates (>47%), followed by cows with fewer than four lactations (43%), then older cows (32%).28 Heat Stress and Loss of Embryos
The poorer conception rates under heat stress usually are attributed to reproductive failure in the female. The number of normal embryos are 23% lower and the number of retarded embryos are 25% higher in heat stressed heifers than in controls.48 Similar numbers of ova are unfertilized. Ulberg and Burfening60 showed that the developmental stages of fertilized egg cleavage are hampered by high temperatures but fertilization rate is not. Their studies also show that sperm cells collected from males exposed to high temperatures are just as effective in fertilizing ova as those of control males but the embryos fail to develop beyond the implantation stage. In another experiment with Table 2. CONCEPTION RATES OF COWS AND HEIFERS IN SUBTROPICAL CLIMATES (HAWAII) DURING HOT AND COOL MONTHS AND COMPARING MORNING VERSUS LATE DAY BREEDING* Hot versus Cool Months Cows Commercial dairies Research herd Research herd heifers AM
versus
*N
PM
N
Hot
N
Cool
P value
4592 230 110
34.2% 50.6% 63.7%
3297 278 96
20.7% 66.3% 70.8%
<.01 <.01 >.05
Breeding
N
AM
N
PM
P value
7116
30.9%
503
38.8%
<.05
= number
ENVIRONMENTAL STRESS EFFECTS ON BOVINE REPRODUCTION
269
rabbits, they provide evidence suggesting that there are differences in fertility of the bucks under heat stress. Further research is needed to determine whether this phenomenon exists in bulls. Differences in ion concentrations in amniotic and allantoic fluids from 30-day-old embryos from cows subjected to heat stress conditions from days 17 to 30 postbreeding suggest that high temperatures are detrimental to embryos even following maternal recognition of pregnancy.42 Heat stressed gilts reduce the amount of conceptus tissue and alter peripheral estradiol concentrations;64 heat stressed ewes reduce progesterone and prolactin production, 8 resulting in placental stunting as they attempt to cope with the demands of the environment. COLD STRESS
Little is known about the effects of cold environments on reproductive processes. Serum thyroxine and triiodothyronine concentrations increase significantly when animals are in the lower critical temperature zone. 63 This results in increased rumen motility and rate of passage of digesta, leading to an increase in dry matter intake. The higher intake is reflective of the need of the animal to produce more energy for warmth. Under severe cold conditions, therefore, pregnant beef cows on pasture without supplementation may lose substantial body weight, resulting in weaker calves. 38 Dairy cows normally are provided with some form of shelter during the winter months. Although the objective of providing shelter is to provide a comfortable environment for dairy producers, these shelters are sufficient in providing warmth and comfort to the cows. The animals therefore seldom are exposed to environmental zones below the critical limit that will have drastic effects on reproduction. MANAGEMENT ALTERNATIVES TO ALLEVIATE STRESS
Balancing rations to meet the animal's demands is one of the key elements for a successful operation. One must have an understanding of the nutrient availability of feed ingredients as well as the animal's needs under different environments. A cow under heat stress conditions has depressed dry matter intake at the same time it is losing large quantities of sodium, potassium, and chloride because of panting, sweating, and salivation. Rumen pH also may decrease. The supplementation of buffers-e.g., sodium bicarbonate or potassium-may help restore appetite and rumen pH, and may even result in higher milk production. 16, 62 Simple shade shelters, fans, and misters can cool cows readily and result in higher milk production32 and reproduction. 43 A hundred percent of Holstein cows under shade exhibited standing estrus but
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only 27.5% in pens with no shade demonstrated mounting behavior.43 The endocrine profiles from cows housed under shade in the subtropics are similar to those in temperate regions. In almost all cases, these investments 43 pay for themselves rapidly.
SUMMARY
Environmental stress is not limited to climatic factors but extends to nutrition, housing, and any stimuli that demand a response from the animal to adapt to new circumstances. Low energy and low or excessive protein levels in the diet are detrimental to reproduction. Likewise, high ambient temperatures and humidity alter the intricate balance of endocrine profiles, leading to lower intensity of estrous behavior, anestrus, embryonic death, and subsequent infertility. Most of these stress factors can be managed with modern technologies to achieve maximum production. Further research in vitamins and minerals under heat stress may add to the knowledge of efficient livestock production.
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39. Lee CN, Cook DL, Parfet JR, et al: Induction of persistent ovarian follicular structures following administration of progesterone near the onset of estrus in cattle. J Dairy Sci 71:3505, 1988 40. Lee CN, Critser JK, Ax RL: Changes of luteinizing hormone and progesterone for dairy cows after gonadotropin-releasing hormone at first postpartum breeding. J Dairy Sci 68:1463, 1985 41. Lee CN, Vincent DL, Nusser KD, et al: Chemical analyses of allantoic fluid from bovine embryos recovered from dams subjected to nutritional stress. BioI Reprod 40:65, 1989 42. Lee CN, Vincent DL, Weems CW, et al: Chemical constituents of allantoic and amniotic fluid of 30 days old bovine embryos under shade or no shade environment. BioI Reprod 44:173, 1991 43. Lee CN, Vincent DL, Weems CW, et al: Endocrine profiles of lactating cows under shade and no shade environments in the subtropics. HITAHR Res Series #70, 1994, in press 44. Lee DHR: Climatic stress indices for domestic animals. Int J Biometeorol 9:29, 1965 45. Madan ML, Johnson HD: Environmental heat effects on bovine luteinizing hormone. J Dairy Sci 56:1420, 1973 46. Magdub A, Johnson HD, Belyea RL: Effect of environmental heat and dietary fiber on thyroid physiology of lactating cows. J Dairy Sci 65:2323, 1982 47. McCann JP, Hansel W: Relationship between insulin and glucose metabolism and pituitary ovarian function in fasted heifers. BioI Reprod 34:630, 1986 48. Putney DJ, Drost M, Thatcher WW: Embryonic development in dairy cattle exposed to elevated ambient temperatures between days 1 to 7 post insemination. BioI Reprod 34:100, 1986 49. Rabeie HM: Effect of Missouri and Libyan seasonal climate on the reproductive performance of Holstein dairy cattle. MS Thesis. Columbia, MO, University of Missouri, 1983 50. Randel RD: Nutrition and postpartum rebreeding in cattle. J Anim Sci 68:853, 1990 51. Remsen LG, Roussel JD, Karihaloo AK: Pregnancy rates relating to plasma progesterone levels in recipient heifers at day of transfer. Theriogenology 18:365, 1982 52. Sasser RG, William RJ, Bull RC, et al: Postpartum reproductive performance in crude protein restricted beef cows: return to estrus and conception. J Anim Sci 66:3033, 1989 53. Sirois J, Fortune JE: Lengthening the bovine estrous cycle with low levels of exogenous progesterone: A model for studying ovarian follicular dominance. Endocrinology 127:916, 1990 54. Smidt D, Farries E: The impact of lactational performance on postpartum fertility in dairy cows. In Karg H, Schallenberger E (eds): Factors Influencing Fertility in the Postpartum Cow. Current topics in veterinary medicine and animal science. The Hague, Martinus Nijhoff, 20:358, 1982 55. Smith TR: Dairy herd profile summary and analysis. Cornell Univ Anim Sci Mimeo Ser 90:27, 1986 56. Spitzer JC, Niswender GD, Seider GE, et al: Fertilization and blood levels of progesterone and luteinizing hormone in beef heifers on a restricted energy diet. J Anim Sci 46:1071, 1978 57. Stott GH: What is animal stress and how is it measured. J Anim Sci 52:151, 1981 58. Stott GH, Williams RJ: Causes of low breeding efficiency in dairy cattle associated with seasonal high temperatures. J Dairy Sci 45:1369, 1962 59. Terqui M, Chupin D, Gauther D, et al: Influence of management and nutrition on postpartum endocrine function and ovarian activity in cows. In Karg JH, Schallenberger E (eds): Factors influencing fertility in the postpartum cow. Current topics in veterinary medicine and animal science. The Hague, Martinus Nijhoff, 20:384, 1982 60. Ulberg LC, Burfening PJ: Embryo death resulting from adverse environment on spermatozoa or ova. J Anim Sci 26:571, 1967 61. Vincent DL, Nusser KD, Carpenter JR, et al: Nutritional stress alters corpus luteum function during early pregnancy in the bovine. BioI Reprod 40:60, 1989 62. West JW, Mullinix BG, Sandifer TG: Changing dietary electrolyte balance for dairy cows in cool and hot environments. J Dairy Sci 74:1662, 1991
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