AI timing - from oestrus detection to insemination

InCalf's messages

The InCalf Book says that the best conception rates occur when cows are inseminated 4 –12 hours after first standing to be mounted. It recommends inseminating cows at the next opportunity after standing heat is detected. One insemination is recommended except for cows still showing oestrus signs 24 hours after insemination.  See page 110 of The InCalf Book.

What the current scientific literature says

Although conception rates may be reduced in cows inseminated either soon after the onset of oestrus (less than 4 hours) or more than 14 –16 hours after oestrus onset, quite acceptable conception rates can be achieved in herds practising once-daily insemination. Cows should be inseminated at the next opportunity after standing heat is detected.

Research has focussed both on whether conception rates are reduced when insemination takes place too soon and too late after the onset of oestrus. Although embryo quality is better following early insemination, fertilisation rates are higher following delayed insemination (Dalton et al 2001) and both fertilisation and embryonic survival are required for successful establishment of pregnancy.

Delaying insemination for more than 18 –24 hours after oestrus is first observed, reduces conception rates by at least 5 percentage points (Arnott 1961; Foote 1979) and this has been confirmed more recently in InCalf research. Conception rates are lower amongst cows inseminated more than several hours after oestrus signs were last detected (Macmillan and Watson 1975a; Macmillan and Watson 1975b). Recent work even suggests that important reductions in conception rates occur if insemination is delayed more than 14–16 hours after onset of oestrus behaviour (Maatje et al 1997; Dransfield et al 1998).

In early research, conception rates were reduced when insemination took place soon after onset of oestrus. Early Australasian work demonstrated that conception rates were highest when insemination was delayed for 9 –15 hours after cows were first recorded as being in oestrus (Arnott 1961; Macmillan and Watson 1975a; Macmillan and Watson 1975b), even where signs of oestrus were only recorded twice daily (Macmillan and Watson 1975a; Macmillan and Watson 1975b). Effects of insemination early in the oestrus period on conception rates interacted with the fertility of the service bull. Conception rates were similar for early and later inseminations when semen was from bulls with above average fertility but were reduced substantially with early insemination when using semen from low fertility bulls (Macmillan and Watson 1975b). However if signs of oestrus persist 24 hours after insemination, reinsemination is recommended (Freischmann 1990 cited by Gordon 1996).

North American research (Trimberger and Davis 1943; Trimberger 1948, both cited by Nebel et al 1994) was the basis of the AM-PM rule where cows first detected in oestrus in the morning (AM) are inseminated that evening (PM) while cows first detected in oestrus in the afternoon or evening are inseminated next morning (Nebel et al 1994). This rule was designed to ensure insemination of cows was neither too early nor too late in the oestrus period. This guideline has the practical disadvantage that herd management must accommodate insemination of cows twice daily. Thus effects of once-daily insemination have been explored despite the need to inseminate some cows early in the oestrus period. Conception rates were only slightly reduced (2 –3%) (Foote 1979) or were higher (Badinga et al 1985) for cows first seen in oestrus in the morning and inseminated that same morning rather than in the afternoon. In four small randomised studies, conception rates were reduced amongst cows allocated to receive insemination soon after detection relative to when insemination was delayed. However, although reductions of 8 –13% were observed in one trial (Graves et al 1997), decreases of only 1–4% occurred in the other three trials (Gwazdauskas et al 1981; Stevenson et al 1984; Maatje et al 1997). More recent studies suggest that insemination need only be delayed by 4 hours after onset of oestrus behaviour for maximum conception rates (Dransfield et al 1998) and mathematical modelling supports this recommendation (Maatje et al 1997). In commercial herds, oestrus behaviour will have commenced some time before signs are detected. These recent studies suggest that conception rates will not be reduced substantially if cows are inseminated within 6 hours after initial observation of oestrus (Nebel et al 2000). The act of insemination may also hasten ovulation, so minimising reductions in conception rate due to early insemination. Natural mating shortens the interval from end of oestrus to ovulation (Marion et al 1950) and cervical manipulation causes oxytocin release (Hays and VanDemark 1953) and hastens the LH surge in oestrus cows (Randel et al 1973).

Recent work has focussed attention on even modest delays in insemination (Maatje et al 1997; Dransfield et al 1998) and Nebel et al recommended that all cows be inseminated within 6 hours after first observation of oestrus (Nebel et al 2000). This infers that conception rates will be reduced by important amounts both where once- rather than twice-daily insemination is practised and by use of the AM-PM rule. This recommendation is not supported by earlier work using a cross-over design in commercial herds, where conception rates were similar whether performed under once-daily or AM-PM insemination rules (Nebel et al 1994) nor by InCalf research where there were not large differences in conception rates between herds practising once-daily insemination and others using twice-daily insemination. However, given these recent findings, more work is required comparing conception rates under once-daily, AM-PM and twice-daily (insemination within 6 hours) methods.

Nutritional factors may interact with optimal AI timing. Dioestrus is delayed after onset of oestrus when nulliparous heifers in fat body condition experience negative energy balance, possibly due to delayed ovulation (Villa-Godoy et al 1990).

Compiled by Dr John Morton

References
Arnott WJ (1961) Problems of artificial breeding of cattle. Australian Veterinary Journal 36: 140 –145

Badinga L, Collier RJ, Thatcher WW and Wilcox CJ (1985) Effects of climatic and management factors on conception rate of dairy cattle in subtropical environment. Journal of Dairy Science 68: 78 –85

Dalton JC, Nadir S, Bame JH, Noftsinger M, Nebel RL and Saacke RG (2001) Effect of time of insemination on number of accessory sperm, fertilization rate, and embryo quality in nonlactating dairy cattle. Journal of Dairy Science 84: 2413 –2418

Dransfield MBG, Nebel RL, Pearson RE and Warnick LD (1998) Timing of insemination for dairy cows identified in estrus by a radiotelemetric estrus detection system. Journal of Dairy Science 81: 1874 –1882

Foote RH (1979) Time of artificial insemination and fertility in dairy cattle. Journal of Dairy Science 62: 355 –358

Gordon I (1996) Controlled reproduction in cattle and buffaloes. Cab International, Wallingford UK

Graves WM, Dowlen HH, Lamar KC, Johnson DL, Saxton AM and Montgomery MJ (1997) The effect of artificial insemination once versus twice per day. Journal of Dairy Science 80: 3068 –3071

Gwazdauskas FC, Lineweaver JA and Vinson WE (1981) Rates of conception by artificial insemination of dairy cattle. Journal of Dairy Science 64: 358 –362

Hays RL and VanDemark NL (1953) Effect of stimulation of the reproductive organs of the cow on the release of an oxytocin-like substance. Endocrinology 52: 634 –637

Maatje K, Loeffler SH and Engel B (1997) Predicting optimal time of insemination in cows that show visual signs of estrus by estimating onset of estrus with pedometers. Journal of Dairy Science 80: 1098 –1105

Macmillan KL and Watson JD (1975a) Factors influencing A.B. conception rates. V. Cow age and stage of oestrus at insemination. New Zealand Journal of Experimental Agriculture 3: 29 –35

Macmillan KL and Watson JD (1975b) Fertility differences between groups of sires relative to the stage of oestrus at the time of insemination. Animal Production 21: 243 –249

Marion GB, Smith VR, Wiley TE and Barrett GR (1950) The effect of sterile copulation on time of ovulation in dairy heifers. Journal of Dairy Science 33: 885 –889

Nebel RL, Dransfield MG, Jobst SM, Bame JH, Forsberg M, Greve T, Gustafsson H, Katila T, Kindahl H and Ropstad E (2000) Automated electronic systems for the detection of oestrus and timing of AI in cattle. Animal Reproduction Science 60 –61: 713 –723

Nebel RL, Walker WL, McGilliard ML, Allen CH and Heckman GS (1994) Timing of artificial insemination of dairy cows: fixed time once daily versus morning and afternoon. Journal of Dairy Science 77: 3185 –3191

Randel RD, Short RE, Christensen DS and Bellows RA (1973) Effects of various mating stimuli on the LH surge and ovulation time following synchronization of estrus in the bovine. Journal of Animal Science 37: 128 –130

Stevenson JS, Schmidt MK and Call EP (1984) Gonadotropin-releasing hormone and conception in Holsteins. Journal of Dairy Science 67: 140 –145

Villa-Godoy A, Hughes TL, Emery RS, Stanisiewski EP and Fogwell RL (1990) Influence of energy balance and body condition on estrus and estrous cycles in Holstein heifers. Journal of Dairy Science 73: 2759 –2765