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7. Lactational anoestrus and the effect of weaning


7.1 Early weaning
7.2 Temporary weaning
7.3 Partial or restricted suckling
7.4 Implications of strategic weaning and partial suckling
7.5 Possible physiologic basis of lactation anoestrus and possible hormonal initiation of cyclicity
7.6 References

The postpartum anoestrous period is longer in suckled or intensively milked animals (Morrow et al, 1969). Continuous suckling delays the return to oestrus in taurine (Laster et al, 1973) and zebu cows (Fonseca et al, 1981; Bastidas et al, 1984; Wells et al, 1986) and results in depressed pregnancy rates (CIAT, 1974). Suckling tends to suppress growth of follicles (Carter et al, 1980) and blocks ovulation (Spicer and Echternkamp, 1986). However, neither the presence of the calf nor frequent milking appears to block the secretion of LH (Williams et al, 1987). Partial or restricted suckling and early or temporary weaning (also called strategic weaning) can reduce the postpartum anoestrous period and improve pregnancy rates (Montoni and Riggs, 1978; Reeves and Gaskin, 1981).

7.1 Early weaning

Early weaning can be particularly useful during periods of feed shortage or when the quality of feed available is low. It allows dams a chance to recover body condition and reconceive, and tends to reduce mortality among cows.

Early weaning (2.7 vs 9 months) increased the pregnancy rate in range cattle in Colombia from 21 to 96% (CIAT, 1974). Maree et al (1974) found that early weaning (2 vs 7 months) reduced the postpartum anoestrous period from 81 to 71 days and increased the average daily weight gain of the cows to first postpartum oestrus from 197 to 352 g. Separating the calf from its dam at 3 days old reduced the postpartum anoestrous period to 47 days and increased average daily gain to 744 g.

Cows whose calves die at or soon after delivery tend to calve every year. Thorpe et al (1981) noted that cows that were not lactating at the beginning of the breeding period had a conception rate of 89%, compared with only 40% among those that had calved late the previous season and still had a calf at foot. Other studies have made similar findings (Wiltbank and Cook, 1958; Rose et al, 1964; Saiduddin et al, 1967; Smith and Vincent, 1972; Laster et al, 1973; CIAT, 1976; Holness et al, 1978; Espaillat et al, 1979; Blantzer, 1982; Moore et al, 1983; Bastidas et al, 1984).

7.2 Temporary weaning

Temporary weaning involves the separation of the calf from its dam for a short period during lactation. Taurine cows have been observed to come in heat when their calves are temporarily weaned 40 to 50 days postpartum. The first oestrous cycle after parturition is often short (Edquist et al, 1984), even if it is due to temporary or early weaning.

Cows ovulate at their first oestrus after weaning their calf, and the ova released can be fertilised (Ramirez-Godinez et al, 1982). However, the corpus luteum tends to be short-lived, and regresses before the conceptus can block the release of prostaglandin and the pregnancy is not maintained. Hormone therapy has been used to try to extend the life-span of the corpus luteum (Entwistle, 1983). Treating cows with progesterone 48 to 72 hours before removing their calves reduces the occurrence of short oestrous cycles and increases the proportion of cows that conceive.

Reports on the effects of temporary weaning are mixed. Some studies report restoration of oestrus within a few days of removing the calf (Rose et al, 1964; Symington and Hale, 1967), whereas others show that oestrus does not occur in response to temporary weaning (Hearnshaw, 1978).

7.3 Partial or restricted suckling

Under partial suckling, the calf is separated from its dam for part of the day to prevent continuous suckling. Partial suckling encourages earlier return to oestrus after parturition and earlier conception, and increases conception rates relative to continuously suckled cows (Table 31) (Britto, 1974; Montoni and Riggs, 1978; Fonseca et al, 1981; Blantzer, 1982; Randel, 1982; Bastidas et al, 1984).

Table 31. Effects of restricted suckling or, postpartum reproductive performance of zebu cows


Once-a-day suckling

Continuous suckling

Cows in oestrus by 60 days postpartum (%) (P<0.005)

57

29

Cows in oestrus by 90 days postpartum (%)

74

63

Conception rate (%):


at 60 days (P<0.005)

31

12


at 90 days

61

44

Anoestrous period (d) (P<0.05)

57.1 +4.19

72.24 +4.35

Service period (d) (P<0.05)

71.42+3.72

82.27+3.80

Source: Blantzer (1982).

7.4 Implications of strategic weaning and partial suckling

The success of strategic weaning and partial suckling regimes depends largely on how well and economically the weaned calves can be reared.

One issue that needs further study is the optimum age for early weaning, particularly for calves that share their dam's milk with humans. Preston et al (1957) showed that calves could be reared on good quality forage from 3 weeks old, and Roy et al (1955) showed that calves can be successfully weaned at 8 weeks old and reared on grass alone.

The control of milk letdown in zebu cattle needs further investigation so that calves can be weaned early but cows can continue to produce milk for human consumption. Some studies indicate that up to 25% of zebu cows will let down milk without their calf being present (Diop, 1981; Furnemont, 1981). Early weaning with zebu cattle will only be truly feasible if difficulties with milk letdown in the absense of the calf can be overcome.

7.5 Possible physiologic basis of lactation anoestrus and possible hormonal initiation of cyclicity

Although the beneficial effects of strategic weaning and partial suckling are well documented, the physiological mechanisms involved are not clear. Most of the available information is for taurine cattle.

Changes in gonadotrophin hormone levels appear to have some effect. Luteinising hormone (LH) levels are lower during the first week after parturition in suckled cows than in cows that are not suckled (Randel et al, 1976). Cows that are not suckled exhibit episodic surges of LH by 7 days after parturition, whereas suckled cows do not (Carruthers et al, 1977; Forrest, 1979). The frequency and amplitude of these LH peaks, together with reduced sensitivity of the pituitary to LH-releasing hormone may be the cause of inhibition of ovulation in suckled postpartum Holstein cows (Carruthers and Hafs, 1980; Carruthers et al, 1980). High suckling intensity reduces serum LH concentrations (Forrest, 1979). Suckling reduces the concentration of prolactin in the follicular fluid and inhibits release of LH from the pituitary following treatment with gonadotrophic-releasing hormone (GnRH) (Kaltenbach and Dunn, 1980).

The length of the postpartum anoestrous period in beef cattle is negatively correlated with basal LH concentrations and is positively correlated with the number of prolactin peaks (Chang et al, 1981). Suckling suppresses the release of gonadotrophin from the pituitary; removing the calf removes this suppression and hence allows follicles to develop in the ovaries (Carter et al, 1980).

Suckled cows remain anoestrous longer when poorly fed than when well fed (Fonseca et al, 1981). Hansel and Alila (1984) stated that the primary causes of postpartum anoestrus in cows in the tropics are poor management, disease and malnutrition, rather than a basic inability of the reproductive tract to function efficiently. Sound management practices tend to shorten the anoestrous period (Tevitt et al, 1977).

7.6 References

Bastidas P. Troconiz J, Verde O and Silva 0. 1984. Effect of restricted suckling on ovarian activity and uterine involution in Brahman cows. Theriogenology 21: 525-532.

Blantzer J S. 1982. Influence of heifer development, calving and suckling manipulation on reproduction in primiparous Brahman percentage cows. Dissertation Abstracts International 43: 1747.

Brito R. 1974. A study of the effects of the reduction in the time spent by zebu calves with their dams on sexual activity of the dams and on growth of calves. Revista Cubana Ciencias Veterinairias 5: 23-30 (Animal Breeding Abstracts 45: 5941).

Carruthers T D and Hafs H D. 1980. Suckling and four-times daily milking: Influence on ovulation, estrus and serum luteinizing hormone, glucocorticoids and prolactin in postpartum Holsteins. Journal of Animal Science 50: 919-925.

Carruthers T D, Kosugiyama M and Hafs H D. 1977. Effect of suckling on interval to first postpartum ovulation and on serum luteinizing hormone and prolactin in Holsteins. Journal of Animal Science 45 (Supplement 1): 142 (Abstract).

Carruthers T D, Convey E M, Kesner J S. Hafs H D and Cheng K W. 1980. The hypothalamo-pituitary gonadotrophin axis of suckled and nonsuckled dairy cows postpartum. Journal of Animal Science 51: 949-957.

Carter M C, Dierschke D J. Rutledge J J. and Hauser E R. 1980. Effect of GnRH and calf removal on pituitary ovarian function and reproductive performance in postpartum cows. Journal of Animal Science 51: 903.

Chang C H. Gimmenez T and Henricks D M. 1981. Modulation of reproductive hormones in young beef cows postpartum. Journal of Reproduction and Fertility 63: 31-38.

CIAT (Centro Internacional de Agricultura Tropical). 1974. Beef production systems. In: Annual Report 1974. CIAT, Apartado Aereo, Cali, Colombia. pp. 151.

CIAT (Centro Internacional de Agricultura Tropical). 1976. Beef production programme. In: Annual Report 1976. CIAT, Apartado Aereo, Cali, Colombia. pp. C1-C75.

Diop M. 1981. The adaptation of zebu cows (Bos indicus) to machine milking: Results of the first trials with Pakistan zebu in Senegal. Thesis, University of Dakar, Senegal. 84 pp. (Dairy Science Abstracts 45: 5362).

Edquist L E, Frederiksson G. Kindhal H. Larson K and Madej A. 1984. Short estrous cycles postpartum in cattle. In: The use of nuclear techniques to improve domestic buffalo production in Asia. International Atomic Energy Agency, Vienna, Austria. pp. 79-83.

Entwistle K W. 1983. Factors influencing reproduction in beef cattle in Australia. AMRC Reviews No. 43. Australian Meat Research Committee, Sydney, NSW, Australia. 30 pp.

Espaillat J M, Gravelay C, Giraldez J, Harqus W and Santhirasegaram K. 1979. Effect of first crop pasture on growth and sexual development in zebu heifers. Memoria, Asociacion Latinoamericana de Produccion Animal 1 4: 117.

Fonseca V, Norte A, Chow L and Lima O. 1981. Effects of suckling intensity on postpartum reproductive efficiency of zebu (Bos indicus) cows. Arquivos de Escola Veterinaria da Universidade Federal de Minas Gerais 33: 165-171.

Forrest P K. 1979. Effect of variable suckling intensity upon serum luteinizing hormone in brangus heifers and estrogen administration upon serum luteinizing hormone in Brahman cows. M.S. thesis, Texas A M University, College Station, Texas, USA. 51 pp.

Furnemont A. 1981. The Ankole: A dairy breed? Development, aspirations and its place in Rwanda. Note Technique de Vulgarisation. Institut des Sciences Agronomique du Ruanda, Butare, Rwanda. 33 pp.

Hansel W and Alila H W. 1984. Causes of postpartum anoestrus in cattle in the tropics. In: Nuclear techniques in tropical animal diseases and nutritional disorders. Proceedings of the Consultative Meeting, 13-16 June 1953, Vienna. International Atomic Energy Agency, Vienna, Austria. pp. 21-40.

Hearnshaw H. 1978. Effect of temporary calf removal on oestrous activity in cows. Proceedings of the Australian Society of Animal Production 12: 258.

Holness D H. Hopley J D H and Hale D H. 1978. The effect of plane of nutrition, live weight, temporary weaning and breed on the occurrence of estrus in beef cows during the postpartum period. Animal Production 26: 47-54.

Kaltenbach C C and Dunn T G. 1980. Postpartum estrus in the beef cow. In: Proceedings of the 11th International Congress on Diseases of Cattle. Tel Aviv, 20-23 October 1980. pp. 791-800.

Laster D B. Glimp H A and Gregory K E. 1973. Effects of early weaning on postpartum reproduction of cows. Journal of Animal Science 36: 734-740.

Maree C, Jurriaanse A and Venter H A W. 1974. The occurrence of postpartum anoestrus in Bonsmara cows on supplemented sourveld grazing. South African Journal of Animal Science 4: 181-183.

Montoni D and Riggs J K. 1978. Effect of restricted suckling on yields and reproductive performance in a Brahman herd. Agronomia Tropical 28: 551-571 (Animal Breeding Abstracts 51: 185).

Moore C P. Rocha C M and Da M C. 1983. Reproductive performance of Gyr cows: the effect of weaning age of calves and postpartum energy intake. Journal of Animal Science 5 7: 807-814.

Morrow D A, Roberts S J and McEntee K. 1969. Postpartum ovarian activity and involution of the uterus and cervix in dairy cattle. I. Ovarian activity. Cornell Veterinarian 59: 173-199.

Preston T R. Archibald J D H and Tinkler W. 1957. The digestibility of grass by young calves. Journal of Agricultural Science 48: 259-265.

Ramirez-Godinez J A, Kiracofe G H. Schalles R R and Niswender G D. 1982. Endocrine patterns in the postpartum beef cow associated with weaning: A comparison of the short and subsequent normal cycles. Journal of Animal Science 55: 153-158.

Randel R D. 1982. Effect of once-daily suckling on postpartum interval and cow-calf performance of first calf Brahman x Hereford heifers. Journal of Animal Science 53 755-757.

Randel R D, Short R E and Bellows R A. 1976. Suckling effect and LH and progesterone in beef cows. Journal of Animal Science 42: 267 (Abstract).

Reeves J J and Gaskin C T. 1981. Effect of once a day nursing on rebreeding efficiency of beef cows. Journal of Animal Science 53: 889891.

Rose C J. Christie G J and Conrade A P. 1964. The effect of early weaning on the reproductive efficiency of ranch cattle in southern Rhodesia. Proceedings of the 1st World Conference on Animal Production. Vol. 3: 125.

Roy J H B. Stillam K W G and Palmer J. 1955. The outdoor rearing of calves on grass with special reference to growth and grazing behaviour. Journal of Dairy Research 22: 252-269.

Saiduddin S. Riesen J W. Graves W E, Tyler W J and Casida L E. 1967. Effect of suckling on the interval from parturition to first estrus in dairy cows. Journal of Animal Science 26: 950-951 (Abstract).

Smith L E Jr and Vincent C K. 1972. Effect of early weaning and exogenous hormone treatment on bovine postpartum reproduction. Journal of Animal Science 35: 1228-1232.

Spicer L J and Echternkamp S E. 1986. Ovarian follicular growth, function and turnover in cattle: A review. Journal of Animal Science 62: 428-451.

Symington R B and Hale D H. 1967. The stimulation of sexual activity in lactating Zebu cows. Rhodesia, Zambia and Malawi Journal of Agricultural Research 5: 13.

Tevitt H R. Smith J F and Kaltenbach C C. 1977. Postpartum anoestrus in beef cattle. A review. New Zealand Society of Animal Production 3 7: 109-119.

Thorpe W. Cruickshank D K R and Thompson R. 1981. Genetic and environmental influences on beef cattle production in Zambia. 4. Weaner production from purebred and reciprocally crossbred dams. Animal Production 33: 165-177.

Wells P L, Holness D H. McCabe C T and Lishman A W. 1986. Fertility in the Afrikander cow. 3. Once a day suckling and its effect on the pattern of resumption of ovarian activity and conception rate in early lactation. Animal Reproduction Science 12: 1-12.

Williams G L, Kozirowski M, Osborn R G. Kirsch J D and Slanger W D. 1987. The postweaning rise of tonic luteinising hormone secretion in anoestrus cows is not prevented by chronic milking or the physical presence of the calf. Biology of Reproduction 36: 1079-1084.

Wiltbank J N and Cook A C. 1958. The comparative reproductive performance of nursed cows and milked cows. Journal of Animal Science 17: 640-648.


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