Key Points:

• Cow comfort management and the availability and quality of feed are the most critical factors in getting a good milk response to POSILAC^®.
  
  
• To measure a substantial difference in the bulk tank, at least 30 to 40 percent of the herd needs to be receiving POSILAC.
  
  
• Healthy cows should be started on POSILAC beginning 57-70 days in milk.
  
  
• There is no correlation between body condition score and milk production response to POSILAC.

POSILAC bovine somatotropin can be utilized in all healthy cows beginning 57-70 days in milk. The increase in milk yield following injection is rapid (Figure 1) with the maximum increase in milk occurring after about three to four injections. Milk yield responses average 10 pounds per supplemented cow per day.

Figure 1
Schematic illustration showing 14-day cycle of POSILAC response

It is not possible to select individual cows that respond to POSILAC, since it is impossible to know what the milk yield would have been without the injection. All healthy cows, beginning 57-70 days in milk, are good candidates for POSILAC. In addition to increasing milk yield immediately, feed intake also increases, although this may lag behind the increase in milk by several weeks. The increased nutrient intake is used both to support the increased milk production and to replenish body reserves in the cow (Figure 2).¹

Figure 1
Effects of POSILAC bovine somatotropin

Heifers

Cows

 

In the U.S., POSILAC has been utilized in commercial herds with herd averages ranging from 14,500 to 27,000 lbs/year (Table 1).² There is little relationship between the lactation increase due to POSILAC and the herd average.

Table 1
Milk yield responses (% or lbs/cow/day) to administration of POSILAC bovine
somatotropin (12 weeks) on 29 commercial farms in 10 states

Heifers and mature cows can respond well to POSILAC, although overall heifer response tends to be slightly lower (Table 2). The genetic potential of the cows for milk production is not related to its responsiveness to POSILAC, i.e. genetically superior Holsteins respond in a similar manner to average Holsteins.

Table 2
Milk yield responses (lbs/cow/day) to POSILAC (500 mg) administration for 252 days in heifers and cows

Cows will enter into a POSILAC program at the rate of about 2 percent of the herd per week (assuming a uniform calving pattern). To measure a substantial difference in the bulk tank, at least 30% to 40% of the herd needs to be receiving POSILAC at any given time, and this will take four months to achieve. Alternatively, the monthly DHIA records of individual cows can be assessed. However, care must be taken in their interpretation given the day-to-day variation in the milk yields of individual cows and that the normal decline of the underlying lactation curve is about 10 percent per month.

Although it would be desirable to pre-select cows that would respond maximally to supplementation with POSILAC bovine somatotropin, there is no way to do this. Generally, provided a cow is healthy and not emaciated, then it should be started on POSILAC beginning at 57 - 70 days of lactation. There is no correlation between body condition score and milk production response to POSILAC. However, longer term herd performance is associated with body condition score, particularly at the start of the next lactation. At the initiation of the administration of POSILAC, cows may lose some body condition (1/4 to 1/2 Body Condition Score Point) until the dry matter intake increases to support the increased milk production.

Long-term responses are influenced by the dry matter intake, so focus should be on the availability of feed at all times. General management recommendations can be summarized as follows:

• Cows should not be overcrowded.
  
  
• Ventilation should be adequate. Supplemental ventilation or evaporative cooling may be desirable.
  
  
• Flooring should provide adequate traction without danger of stone bruises.
  
  
• Muddy areas should be cleaned and/or eliminated.
  
  
• Feeder and feeding areas should be designed to make it easy for cows to eat.
  
  
• Keep feed bunks clean to avoid moldy feed buildup.
  
  
• Clean potable water in adequate amounts should be provided at all times. Additional water supplies may be required.
  
  
• High-quality forages should be fed.
  
  
• In hot weather, cows must be protected from the effects of heat. Adequate shade should be provided.
  
  
• Fly control is imperative.
  
  

References

1. Hartnell GF, Franson SE, Bauman DE, Head HH, et al: Long-term evaluation of sometribove, recombinant methionyl bovine somatotropin, in a prolonged release system in lactating dairy cows-production responses in a dose titration study. J Dairy Sci 1991;74:2645.
2. Thomas JW, Erdman RA, Gallon DM, Lamb RC, et al: Responses by lactating cows in commercial dairy herds to recombinant bovine somatotropin. J Dairy Sci 1991;74:945

For more information, read
Adoption of Agricultural Technologies and the Economics of bST

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