Measurements can be performed in the farm with the use of ketone strips or digital devices. Blood samples should be collected from cows about 5 hours after the last feeding to catch the peak BHBA concentration. For BHBA, a minimum of 12 cows should be sampled. The target group for this test should be cows between 5 and 50 days in milk (DIM).
Thus, consultants and producers can track the percentage of cows with BHBA greater than 1,400 μmol/L. Preferably, no more than 10% of the cows should present high BHBA levels in blood.
NON STERIFIED FATTY ACIDS (NEFAS)
Presence of NEFAs in the blood is a direct indicator of massive fat mobilization, which suggests that cow demands for energy are much higher than supplied in the diet; therefore, the NEFA analysis can indicate whether a herd has abnormal levels of negative energy balance.
We should not track mean values, but rather the proportion of cows above a certain threshold level of NEFAs. For cows from 2 to 14 days before calving, the adequate threshold value is 0.400 mEq/l. In other words, we need to calculate the proportion of cows with NEFA levels higher than this threshold in the prepartum. It is recommended that no more than 10% of the cows are above this threshold.
Blood samples for NEFA analysis should be collected just before the feeding time. If a cow calves soon after sample collection (less than 2 days) her sample should be interpreted with caution or removed from analysis. The recommended minimum sample size is 12 cows.
Ruminal pH can be evaluated to measure the risk for sub acute ruminal acidosis (SARA) in the herd. It is being shown that herds with higher proportion of cows with ruminal pH ≤ 5.5 have lower fertility.
Ruminal samples can be collected at five (5) hours after the last feeding, from cows at 5 to 150 DIM, with appropriate needle and syringe as described by Garrett et al., 1999.
No more than 25% of the cows should present ruminal pH ≤ 5.5. f more than 25% of the cows have uminal pH ≤ 5.5, it means that this given herd is going through some risks related with subclinical acidosis and changes in diet should be performed. For SARA a minimum of 12 cows should be sampled.
MILK UREA NITROGEN (MUN) OR BLOOD UREA NITROGEN (BUN)
It is widely known that high levels of MUN are associated with lower fertility in dairy cows. In general, most of the research articles show that if MUN is ≥ 18-19 mg/dL, conception is generally compromised, whereas optimal MUN values for lactating dairy cows are 12-16 mg/dL.