TAKE HOME MESSAGES
- As little as 21 days of 4X milking early in lactation can increase yield throughout lactation.
- Prolactin increases at milking may be the mechanism to enhance mammary cell growth and thus milk yield.
- Frequent milking early in lactation can improve yields throughout that lactation with little additional cost.
INTRODUCTION
Increasing the frequency of milk removal increases milk production in cattle as it does in many species (6). Indeed, this is a common management approach to maximize production per cow and fully optimize capital investment in machinery and facilities. One obvious drawback is the increase in variable costs, mainly labor, required to reap the higher yield of milk. Traditionally, this technique has been employed throughout lactation, but recent evidence suggests that frequent milking appropriately timed within the lactation cycle can have persistent effects, and thus eliminate some of the higher costs while maintaining higher yields. This paper reviews the physiology behind the response, expected outcomes from increased milking frequency, and proposes easily adopted strategies to exploit frequent milking during early lactation to improve overall yields.
Increasing the number of milkings from 2 (2X) to 3 (3X) each day increases production in cattle across a range of production levels (4). It is of interest that this appears to be a fixed response. That is, cows producing 40 pounds/day when milked 2X will increase production about 8 pounds/day when shifted to 3X; cows producing 80 pounds/day would also increase production by 8 pounds/day. So management decisions based on percentages can be deceiving, as the absolute response is not very different across production levels yet the percentage response actually decreases as average milk yield increases!
RESEARCH ON MILKING FREQUENCY IN EARLY LACTATION
Israeli workers (1) observed higher production in cows milked 6X relative to 3X during the time that milking frequency was increased (Table 1). However, there was a striking persistency of the production response following a return to 3X from 6X. Cows milked 6X for the first 42 days of lactation continued to yield more milk even after milking frequency was reduced to 3X. Milk composition, though somewhat low, was not different between groups. Relative to those milked 3X, dry matter intake was increased in 6X cows. Cows milked 6X experienced a longer delay in return to positive energy balance and a longer time at a body condition score below 2.5 than those cows milked 3X. Collectively, cows milked 6X for only the first 6 weeks in milk had greater milk yield and feed efficiency for the entire lactation when compared with those milked 3X.
Table 1. Daily milk, components and lactation yield of cows milked 3X or 6X for the first 42 days of lactation and then 3X for the remainder of 305 day lactation. Daily yields were recorded during treatment (week 1-6) and after treatment for 12 weeks (week 7-18). Complete lactation records were from DHI testing (305 d). Data from Bar-Peled et al., 1995 (1).
| 3X | 6X | |
| Milk, week 1-6, lbs | 77.8 | 94.0a |
| Fat %, week 1-6 | 3.28 | 3.16 |
| Protein %, week 1-6 | 3.13 | 3.07 |
| Milk, week 7-18, lbs | 82.5 | 93.7a |
| Fat %, week 7-18 | 2.80 | 2.81 |
| Protein, week 7-18 | 2.76 | 2.79 |
| Milk, 305 d, lbs | 19,832 | 23,100a |
aSignificantly greater than 3X controls, P<.05
A recent experiment in Maryland (5) confirmed under field conditions that milking cows 6X in early lactation produced persistent improvements in milk yield even after cows returned to 3X. For the first 42 days of lactation, cows were milked 3X at 8 hr intervals or 6X at approximately 4-5 hr intervals. After d 42 all cows were milked 3X for the rest of the study which lasted through 38 weeks of lactation. Relative to those milked 3X, multiparous cows milked 6X produced more milk throughout the study. On a percentage basis, milkfat was unaffected by treatment whereas milk protein was lower; protein and fat yield, however, were improved overall by 6X treatment. In addition, there was no adverse effect on reproduction as conception rate to the first synchronized ovulation was not different between groups.
Table 2. Milk, components and conception rate of cows milked 6X or 3X for the first 42 days of lactation. Data from Henshaw et al., 2000 (5).
| Treatment | Milk (lbs/d) | Fat (%) | Protein (%) | Conception Rate (%)a |
| 3X | 84.2 | 3.87 | 2.98 | 23.3 |
| 6X | 90.6b | 3.92 | 2.87c | 31.0 |
aResults from synchronized breeding at 69 to 76 days in milk. bSignificantly greater than 3X controls, P<.01. cSignificantly lower than 3X controls, P<.05.
PHYSIOLOGY BEHIND THE RESPONSE
There are two physiologic explanations for the impact of frequent milk removal on production. The first is the potential physical effect of increasing intramammary (IM) pressure to reduce the rate of milk synthesis within mammary epithelial cells. The IM pressure hypothesis suggests that physical forces of milk accumulating within the alveoli causes a compression of the secretory cell and this in turn reduces cellular metabolism and milk component synthesis. Indeed, the milk synthesis rates are fastest immediately after milking and decline with time to about 36 hours when secretion essentially stops. More recently a hormone-like factor, secreted by mammary epithelial cells, has been implicated as a suppressor of milk synthesis. This feedback inhibitor of lactation (FIL) acts in a self-limiting fashion to reduce milk synthesis. As milk accumulates in the gland between milkings, so does FIL accumulate, and thus it increasingly suppresses milk component production by the very cells that secrete it. Both IM pressure and FIL would be reduced by more frequent milking, and increases in milk yield would result relative to less frequent milking. However, these mechanisms may not be responsible for the impact of frequent milking during early lactation, as those responses persist in the absence of continued high frequency milk removal.
A more general response to milking frequency is the effect on secretion of prolactin. Circulating concentrations of prolactin increase acutely after each milking. Evidence from our work with photoperiod, another factor that can be used to manipulate prolactin, suggests that an increase in prolactin early in lactation may increase the number of secretory cells within the mammary gland for that lactation (3). It appears that in mammary cell growth reaches a peak in late pregnancy but continues into the first few weeks of lactation. Because milk production is a function of the number of mammary secretory cells (2), starting lactation with a greater number of secretory cells should increase yield. More importantly, this increase would be expected to persist because cell loss is a constant throughout lactation. Prolactin is thought to have a stimulatory effect on mammary cell development, and the higher prolactin in response to more frequent milking early in lactation may thus explain the persistent effect of this practice on yield.
Table 3. Predicted milk response and potential economic benefit from derived from milking all cows 4X for the first 21 days of lactation in a 120 cow herd.
| 3 lbs | 6 lbs | 9 lbs | |
| Labora | $.11 | $.11 | $.11 |
| Feedb | .09 | .18 | .27 |
| Suppliesc | .05 | .05 | .05 |
| Milk revenued | .33 | .66 | .99 |
| Marginal profit/cowe | .08 | .32 | .56 |
| Marginal profit/farmf | $2,928 | $11,712 | $20,496 |
aLabor cost of $20/hour; 4 hours/cow/lactation. bDry matter at $.06/lb; 0.5 lb DM for each lb of milk increase. cCost for supplies for an extra 42 milkings distributed over entire 305 day lactation. dMilk at $11.00/cwt. eEstimate is for each day of a typical 305 day lactation. fCalculated from profit/cow for 305 day lactation for 120 cow herd.
MANAGEMENT SUGGESTIONS
Increasing the frequency of milking early in lactation is simple to implement. In a 2X or 3X scheme, fresh cows can be milked first and last at each milking to achieve either a 4X or 6X frequency. While this may not yield exact 6 or 4 hour intervals between each milking, it is likely to provide appropriate stimulation such the persistent increases in milk production are observed. The question then becomes one of duration that is, how long should the producer milk at increased frequency? Evidence from recent experiments suggests that the increased frequency need only be imposed for the first 21 days of lactation. For example, if typically cows are milked 2X at 12 hr intervals, then fresh cows only could be milked at the beginning and end of each milking. In a herd of 120 milking cows, estimate that 10 cows would calve each month, so at any time 7-8 cows would be milked 4X. This would not require any additional labor to be hired, yet the research indicates that an amount of production close to continuos 3X milking can be achieved. Table 3 presents expected returns on adopting early lactation frequent milking in a typical 120 cow herd. Assuming a 6 pound/cow/day response yields an additional potential profit of $97.60/cow with a milk price of $11.00.
Source: Illinois.edu
