Spaying of Heifers

John Cavalieri - James Cook University - Meat and Livestock Australia Limited

Type: Research Paper
Knowledge level: Advanced

Farm Table says:

This research article looks at chemical sterilization as an alternative to spaying of heifers. Treatments used were not able to sterilise most Bos indicus heifers but treatment with CaCl2 has the potential to cause complete ovarian atrophy without causing detectable pain.


Chemical sterilization as an alternative

What is the problem?

Spaying of female cattle is used within the Northern Australian beef cattle industry to prevent unwanted pregnancies and improve economic returns from females that are surplus to breeding requirements.

This research goal was to investigate the effectiveness of three potential chemosterilants to sterilize Bos indicus heifers after intraovarian administration.

What did the research involve?

3.1 Approvals
– The experimental procedures were approved by the James Cook University Animal Ethics Committee.

3.2 Animals
– Brahman heifers, 23 to 26 months of age (n=40) were obtained for the An observational cross-sectional study from the James Cook University Tropical Veterinary Research Station, Fletcherview (latitude 19°53’4″”S; longitude 146°10’43″”E) located in the dry tropics, of Northern Queensland. Heifers were transported to, and maintained at the James Cook University campus (latitude 19o 19’37’’S, longitude 146o 45’27”E) for at least 3 weeks prior to commencing treatments and at least 2 weeks after completing treatments. Heifers were divided into 5 replicates of 8 animals, with 2 animals/treatment within each replicate (n = 10/treatment.

3.3 Treatments
-Heifers had their oestrous cycles synchronized by administration of an intravaginal progesterone releasing insert (CIDR®, Zoetis Australia, West Ryde, NSW) and administration of oestradiol benzoate (1 mg/500 kg IM, Cidirol, Genetics Australia, Bacchus Marsh, Vic) at the time of device insertion.

3.4 Blood sampling.
-Blood samples were collected from the coccygeal vein or artery on the day of administering intraovarian treatments (Day 0) and on Days 2 and 7 following treatment.

3.5 Aversion testing.
-The aversion of heifers to the treatment area was assessed by timing the entry of heifers to the treatment area.
3.6 Heart rate monitoring and video recording of behavior.
-Heifers were acclimatized to individual pens for restraint on two separate days before commencing heart rate monitoring.

3.7 Breeding
– Heifers in each replicate were exposed to carried out using a bull 82 (Replicates 2 and 4) or 84 (Replicates 1, 3 and 5) days after treatment and depending on replicate, the bull was removed between 230 to 246 days after the start of treatment.

3.8 Ovarian histopathology and oocyte counts.
-At the time of slaughter ovaries were either placed on ice and returned to our laboratory for processing (Replicates 1 and 2) or processed at the time of slaughter (Replicates 3 to 5).

3.9 Statistical analyses.
-Repeated measures analysis of variance was used to assess mean heart rates and the area under the curve of heart rates, mean concentrations of haptoglobin and bodyweights over time.

What were the key findings?

4.1 Data omissions.
-Data obtained during replicate one was retained for assessment of bodyweights, behaviour at the time of treatment, pregnancy, concentrations of progesterone, intervals to conception and ovarian characteristics as no significant effects of replicate were obtained for these variables.

4.2 Behaviour associated with treatment.

4.2.1 Behaviour at treatment
-Behaviour recorded at the time of administration was recorded as no visible reaction in 75% of animals that were treated with 25% of animals exhibiting mild struggling only.

4.2.2 Aversion testing and rectal temperatures
-The time required for animals to enter the holding crate and the degree of assistance provided was not affected by treatment, day, replicate and no significant interactions were detected.

4.2.3 Heart rate monitoring
-Mean heart rates were found to differ across days.

4.2.4 Behaviour after treatment
-Behavioural characteristics recorded in heifers during a 90 minute observation period after treatment.

4.3 Haematology, acute phase proteins and anti-Müllerian hormone

4.3.1 Haematology
-Mean total leukocyte counts between Days 0 and 7 following administration of treatments did not differ between treatments.

4.3.2 Acute phase proteins.
-Concentrations of haptoglobin obtained on Days 0 and 7 in heifers in Replicates 2 to 5.

4.3.3 Anti-Müllerian hormone.
-Concentrations of anti-Müllerian hormone between 215 and 222 days after treatment did not differ between treatments.

4.4 Intervals to ovulation and pregnancy.
-Ovulation was detected in every heifer during the monitoring period after treatments were applied.

4.5 Changes in body weight
-Mean body weights over time did not differ between replicates.

4.6 Ovarian characteristics at slaughter.
-Characteristics of ovaries recovered at slaughter from heifers from each treatment group.

5.1 Overall findings
-In order to sterilise female cattle in Northern Australia that are surplus to breeding requirements the ideal treatment would be effective after a single intervention, not have an adverse effect on animal welfare or leave any undesirable tissue residues, be inexpensive and enable animals to be processed in as short a time as possible.

5.2 Ovarian atrophy and mechanism of action
-n this study administration of CaCl2 significantly reduced the paired weight of ovaries compared to heifers treated with saline.

5.3 Animal behaviour
-Treatment with ZG either alone or in combination with CaCl2 in an aqueous base induced changes in behaviour that were consistent with the sensation of pain.

5.4 Heart rates
-Mean heart rates on all of the days on which heart rates were monitored fell within normal reference values for cattle and did not differ between treatments.

5.5 Inflammatory Markers.
-No significant effects of treatment were observed within 7 days of treatment in total white cell counts or concentrations of haptoglobin.

5.6 Anti-Müllerian hormone
-Both the total oocyte count and concentrations of AMH were not significantly affected by treatment.

5.7 Limitations of the study
-This study was the first known attempt to sterilise female cattle by infusing CaCl2 and or ZG. Statistical power was kept to a minimum in case undesirable side effects such as pain occurred in response to treatment.

Final Comment

Treatment with ZG and the combination of ZG and CaCl2 did not affect ovarian mass compared to administration of saline and was associated with behavioral changes that were indicative of pain and, therefore, appear to offer no potential for use as intraovarian chemosterilants in cattle.

2016 - Australia - John Cavalieri - James Cook University - Meat and Livestock Australia Limited
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