Pregnancy diagnosis
Rectal palpation - The four cardinal signs of pregnancy are:
1) Fetal membrane slip - detectable from 30 days to term
2) Amniotic vesicle - palpable from days 30-65 as a movable object in the uterine
lumen - some suggest palpation of the amniotic vesicle during days 33-40 of
pregnancy may induce atresia coli
3) Placentomes - palpable from day 75 to term
4) Fetus - palpable from about day 70 to term
Ultrasonography - not used routinely due to cost and inconvenience of instrumentation
Milk/plasma progesterone - If a cow was in estrus when bred and has a normal
cycle length, elevated progesterone 21-24 days post-breeding is suggestive of
pregnancy.
Accessory sex glands of the bull = seminal vesicles (vesicular glands), ampullae, prostate, bulbourethral glands
Bovine estrous cycle
Puberty occurs at 8-12 months of age and is dependent on body condition, body weight and genetics. You want all heifers bred by 2 years of age but want them bred when at a large enough body size to minimize dystocia.
Estrous cycle length = 21 days. Length of standing heat = about 1 day, ovulation occurs 24-30 hours after estrus onset.
Signs of heat in cows - The primary sign is standing to be mounted by other cows. Secondary signs include mounting other cows, restlessness, and mucoid discharge from the vulva.
Gestation length = 280 days
Production medicine
Desired calving interval is 12-13 months so cows must become pregnant within 85-115 days after calving. You must allow the cow a 40-50 day voluntary waiting period before breeding, leaving only a 35-75 day breeding period (1-3 estrous cycles). Poor heat detection is a common cause of apparent infertility in a given cow and a common cause of poor profitability on a given farm.
Retained fetal membranes
Fetal membranes are defined as retained if they are not expelled within 12 hours of calving. Possible causes for retention include abortion, premature birth, low Vit E / selenium in the ration, dystocia, milk fever (hypocalcemia), heat stress, and infection (placentitis). Methods of treatment include non-intervention, manual removal (historical treatment, no longer recommended), intrauterine antibiotic infusion (tetracycline commonly used), and oxytocin. Treat cows that are systemically ill with parenteral antibiotics (penicillin, ceftiotur) and non-steroidal anti-inflammatory drugs.
Cystic ovarian disease
Cystic ovarian disease is defined as persistence of a follicle-like structure on the ovary greater than 2.5 cm in diameter for more than 10 days in the absence of a palpable or visible CL. Cows present in anestrus (80%) or as nymphomaniacs (20%). Diagnose by palpation or ultrasound, and measurement of progesterone in serum (high if luteal cyst, low if follicular cyst). Treatments include spontaneous recovery, manual rupture (not recommended - may cause adhesions), exogenous LH or GnRH for follicular cysts, PGF2-alpha or an analogue (cloprostenol) for luteal cysts
Infectious bovine rhinotracheitis (IBR)
Herpesvirus. IBR can cause infectious pustular vulvovaginitis, balanoposthitis, and abortion in the last trimester with fetus autolyzed when expelled. IBR can be diagnosed from the abortus by demonstration of focal necrosis and intranuclear inclusions in the liver, kidneys, and adrenal glands and can be demonstrated by virus isolation or fluorescent antibody testing. Prevent IBR by vaccination after six months of age but well before first breeding with annual revaccination. Do not vaccinate purebred bulls and breeding bulls (limits sale of animal or semen if seropositive).
Bovine viral diarrhea (BVD)
Togavirus. BVD can cause abortion at any stage of gestation; abortion is most common if the cow is infected early in pregnancy. Calves born live to infected cows may have cerebellar degeneration and/or ocular defects. Prevent by vaccinating after 6-8 months of age. Do not vaccinate with a MLV product in pregnant cattle and do not vaccinate bulls (see above).
Brucellosis
Brucella abortus. Disease is characterized by abortion after the 5th month of pregnancy with sequelae of retained fetal membranes and metritis. Due to test and slaughter programs and vaccination, incidence is greatly reduced in the United States. Minnesota was certified brucellosis-free in 1984.
Causes of abortion in cows
Non-infectious = poor nutrition, developmental abnormalities of fetus, high environmental temperature, toxins (sweet clover, Ponderosa pine)
Infectious = brucellosis, leptospirosis, IBR, BVD
Freemartin = sexually abnormal female calf born co-twin to a male calf. Developmental abnormalities of the female calf are due to exposure to male hormones during embryogenesis.
Milk fever = hypocalcemia - signs include anorexia, recumbency. Treat
with IV calcium (auscult heart whenever giving calcium IV, stop administration
if hear tachycardia or bradycardia, any arrhythmia).