In desi cow and buffalo reproduction is govern by photoperiod, means it is depend on day length. Cows breed during long days (Month of June) and buffalo breeding during short days Oct to Dec. However, exotic cow breed any time.
The temperature, humidity day length and nutrition play important role. So it is complex phenomena. However, selenium and vitamin E seems to play important role in overcoming repeat breeding. Macro micronutrient and vitamins in optimum amount are also important. However low producers create fewer problems than the high producing cows.
In this article I will only take cross breed cow of Jersey or Holstein cow. The problem of repeat breeding is more serious in Holstein than Jersey. The age of first conception is also shorter in Jersey than Holstein. Jersey clave at about 24 months whereas, Holstein clave at 30 to 35 months. If female calf is born in September it takes less time than it is born in summer months. It is because in winter months due to low temperature cows grow faster than in summer month. Cow calves in nine month and ten days and it comes in heat within month of calving. So it should fall pregnant within 60 days of calving. In this way it will calve at same time every year. Once cow is pregnant it should be dried at seven month of pregnancy it improve the health of cow in term of immunity and reproductive health. For avoiding reproductive probelmes after calving it can be giving Tefrocef of MSD or Ceftiofer sodium @ 2 mg per kg for 5 days it help curing matritis, vaginitis or prolaps related problems because it attacks Arocanobaeterium pyogenes, Fusobacterium necrophorium and Bacterodes. This antibiotic, Ceftiofer has zero with drawl periods. So you need not discard milk. For bring cow in heat after calving you should use Prostaglandins Estrumate or Lutalyas on 10th day of calving and do not inseminate again give prostaglandins of on 10th day and if cow comes in heat inseminate. Use receptal (2.5 ml I/M) at AI (Article Insemination) again on 10th day after AI give receptal. This will increase changes of conception. Six hour and six days are critical for implantation so keep cow cool below 200 C. At 450c and high humidity there is no conception. Pseudo pregnancy or retention of corps lutetium is a big problem. The cow does not come in heat and it is not pregnant. If cow is not coming in heat it does not mean it is pregnant. Pregnancy test is must. This can be done 35 days. But pregnant animals do come in heat. About 30% cows are pregnant and they do come in heat. Second insemination the AI gun should not pass cervix. If cow is not pregnant and is not coming in heat. It should be given Estrumate or Lutalyas and on second heat it should be inseminated.
For making calf a year a reality estrus management in cow is necessary. So follow the under giving plan. The same plan can be followed for synchronization of estrus in by herd.
Making Calf A Year Really
Taken from Internet
Taken from MSD Ruminant Product Information Book.
Sometimes cow come in heat or their heat in irregular. This is sign of cystic ovary and veterinarian can diagnose. In this case high dose (5 mI/M) recptal should be tried.
For your reference from humidity temperature chart you may know level of stress. This will help you a lot.