**1. Introduction**

234 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

0020-7128

London.

ISSN 0022-0302

Vol. 39, pp. 233-237, ISSN: 0001-2351

*Dairy Science,* Vol. 74, pp. 3583-3597, ISSN 0022-0302

Desert. . *Journal of Dairy Science,* Vol. 78, pp. 620-624, ISSN 0022-0302

grazing Holstein cows. Int J Biometeorol. 52:239-247, ISSN: 0020-7128

Solomon, R.; Miron, J.; Ben-Ghedalia, D. & Zomberg, Z. (1995). Performance of high producing dairy cows offered drinking water of high and low salinity in the Arava

Valtorta, S.E. & Gallardo, M.R. (2004). Evaporative cooling for Holstein dairy cows under grazing conditions. *International Journal of Biometeorology,* Vol. 48, pp. 213-217, ISSN:

Valtorta SE, Gallardo MR, Sbodio OA, Revelli GR, Arakaki C, Leva PE, Gaggiotti M, Tercero EJ. 2008. Water salinity effects on performance and rumen parameters of lactating

Valtorta, S.E.; Gallardo, M.R.; Castro, H.C. & Castelli, M.E. (1996). Artficial shade and supplementation effcets on grazing dairy cows in Argentina. *Transactions of the ASAE,* 

Van Soest, P.J.; Robertson, J.B. & Lewis, B.A. (1991). Methods for dietary fiber, neutral detergent fiber, and non-starch polysaccharides in relation to animal nutrition. *Journal of* 

Van Soest, P.J. (1994). Funtion of the ruminant forestomach. In: *Nutritional ecology of the ruminant. Second Edition,* University Press, ISBN: 080142772X, Cornell Ithaca and

Wilks, D.L.; Coppock, C.E.; Lanham, J.K.; Brooks, K.N.; Baker, C.C.; Bryson, W.L.; Elmore, R.G. & Stermer, R.A. 1990. Responses of lactating Holstein cows to chilled drinking water in high ambient temperatures. *Journal of Dairy Science,* Vol. 73, pp. 1091-1099, Manipulation of the lactation curve by increasing peak milk production and (or) lactation persistency has consistently been a focus of both researchers and dairy producers. One of the key findings that has enabled manipulation of lactation performance is that the milk yield of dairy cows is responsive to demands of offspring or milk removal; hence milk production can be increased by frequent milking or suckling. Early studies illustrated the galactopoietic effect of frequent milking during the entire lactation, with three times daily milking increasing milk yield by up to 20% relative to twice daily milking. Research using nurse cows revealed a long-term increase in milk production when cows and heifers were allowed to suckle a calf during the first 8 to 10 wk of lactation (Everitt & Phillips, 1971; Edmunds, 1977; Fulkerson, 1981). The results of these experiments laid the groundwork for current research, which has identified a time during early lactation wherein the mammary gland of dairy cows is especially receptive to the stimulus of frequent milking. More recently, it has been established that frequent milk removal (three or more times daily) for a short duration within the first three weeks of lactation can increase milk production through the remainder of lactation (Hale et al., 2003; Dahl et al., 2004b; Wall & McFadden, 2007b). Since the establishment of the galactopoietic effect on milk production, several experiments have been conducted to identify the factors that regulate the milk yield response. These reports have documented consistent responses to increased milking frequency; however, questions remain about the mechanisms involved in regulation of milk production efficiency.

## **1.1. Frequent milking or suckling increases milk production**

As previously indicated, frequent milking of dairy cows has emerged as an effective management tool for dairy farmers to increase milk production efficiency. Although it is a

relatively novel management practice, the original interest and research in this area dates back to the late 1800's (Hills, 1890; 1898). Despite considerable variation in the magnitude of the milk yield response, it was recognized long ago that thrice-daily milking (**3X**) increased milk production relative to twice-daily milking (**2X**), and that frequent milking could be a profitable management tool if costs associated with the extra milkings are outweighed by the value of additional milk obtained (Riford, 1922; Dahlberg, 1924). Cows milked 3X generally produced about 20% more milk than those milked 2X, and milk production could be increased another 7% by milking four times daily (**4X**) instead of 3X (Woodward, 1931). Modern-day adjustment factors used to compare milk production of cows milked 2X to those milked 3X range from 12-14%, depending on the parity of the cow (VanRaden et al., 1999).

Much of the work on frequent milking for the entire lactation was conducted during the 1980s and 1990s, when there was great interest in switching milking regimes from 2X to 3X in order to increase milk production efficiency (Table 1). A typical response to 3X milking is illustrated in Figure 1, which shows the lactation curves of cows milked 2X or 3X for the entire lactation (re-drawn from Amos et al., 1985). Three-times daily milking increased milk production both at peak and through the entire lactation. Persistency of the lactation curve was also slightly increased, but this effect disappeared after approximately 180 DIM. In summaries of DHIA records, the increase in milk production with 3X was 13, 12, and 16% compared to 2X (Allen et al., 1986; Gisi et al., 1986; Smith et al., 2002). These reports were obtained from mostly Holstein herds, or combined Holstein and Jersey herds. Culotta and Schmidt (1988) suggested that smaller dairy breeds do not respond as well to frequent milking as larger breeds. Consistent with that hypothesis were observations of Campos et al. (1994), that relative to 2X, 3X increased milk production by 17.3 and 6.3% in Holsteins and Jerseys, respectively. In contrast, Copeland (1934) observed an impressive 21 and 19% increase in milk and fat production, respectively, from Jerseys milked 3X compared to those milked 2X. In addition, they reported a correlation (+.64) between the amount of milk cows produced prior to frequent milking and the magnitude of the response to frequent milking (Copeland, 1934). This led to speculation that higher producing cows better responded to increased milking frequency than did lower producing cows. The existence of such a relationship, however, has not been established. To the contrary, Erdman and Varner (1995) and Stockdale (2006) reviewed the literature on frequent milking, and reported no correlation between previous milk production and the response to changes in milking frequency. Instead, those researchers concluded that there was an incremental milk yield response. Relative to 2X, this fixed milk yield response was -6.2, +3.5 and +4.9 kg/d for once daily milking (**1X**), 3X, or 4X, respectively (Erdman & Varner, 1995). In agreement with this, Peel et al. (1979) estimated that the post-suckling increase in milk production of cows suckled for as little as one week during early lactation was 4.3 kg/d. They went so far as to provide the readers with the following equation to allow prediction of the milk yield response to various suckling regimes:

Increase in milk yield % 4.3 0.8 mean S.E. x number of weeks suckled.

1999).

response to various suckling regimes:

relatively novel management practice, the original interest and research in this area dates back to the late 1800's (Hills, 1890; 1898). Despite considerable variation in the magnitude of the milk yield response, it was recognized long ago that thrice-daily milking (**3X**) increased milk production relative to twice-daily milking (**2X**), and that frequent milking could be a profitable management tool if costs associated with the extra milkings are outweighed by the value of additional milk obtained (Riford, 1922; Dahlberg, 1924). Cows milked 3X generally produced about 20% more milk than those milked 2X, and milk production could be increased another 7% by milking four times daily (**4X**) instead of 3X (Woodward, 1931). Modern-day adjustment factors used to compare milk production of cows milked 2X to those milked 3X range from 12-14%, depending on the parity of the cow (VanRaden et al.,

Much of the work on frequent milking for the entire lactation was conducted during the 1980s and 1990s, when there was great interest in switching milking regimes from 2X to 3X in order to increase milk production efficiency (Table 1). A typical response to 3X milking is illustrated in Figure 1, which shows the lactation curves of cows milked 2X or 3X for the entire lactation (re-drawn from Amos et al., 1985). Three-times daily milking increased milk production both at peak and through the entire lactation. Persistency of the lactation curve was also slightly increased, but this effect disappeared after approximately 180 DIM. In summaries of DHIA records, the increase in milk production with 3X was 13, 12, and 16% compared to 2X (Allen et al., 1986; Gisi et al., 1986; Smith et al., 2002). These reports were obtained from mostly Holstein herds, or combined Holstein and Jersey herds. Culotta and Schmidt (1988) suggested that smaller dairy breeds do not respond as well to frequent milking as larger breeds. Consistent with that hypothesis were observations of Campos et al. (1994), that relative to 2X, 3X increased milk production by 17.3 and 6.3% in Holsteins and Jerseys, respectively. In contrast, Copeland (1934) observed an impressive 21 and 19% increase in milk and fat production, respectively, from Jerseys milked 3X compared to those milked 2X. In addition, they reported a correlation (+.64) between the amount of milk cows produced prior to frequent milking and the magnitude of the response to frequent milking (Copeland, 1934). This led to speculation that higher producing cows better responded to increased milking frequency than did lower producing cows. The existence of such a relationship, however, has not been established. To the contrary, Erdman and Varner (1995) and Stockdale (2006) reviewed the literature on frequent milking, and reported no correlation between previous milk production and the response to changes in milking frequency. Instead, those researchers concluded that there was an incremental milk yield response. Relative to 2X, this fixed milk yield response was -6.2, +3.5 and +4.9 kg/d for once daily milking (**1X**), 3X, or 4X, respectively (Erdman & Varner, 1995). In agreement with this, Peel et al. (1979) estimated that the post-suckling increase in milk production of cows suckled for as little as one week during early lactation was 4.3 kg/d. They went so far as to provide the readers with the following equation to allow prediction of the milk yield

Increase in milk yield % 4.3 0.8 mean S.E. x number of weeks suckled.

**Figure 1.** The effect of frequent milking on milk production of dairy cows. Lactation curves of multiparous cows milked twice (2X) or thrice (3X) daily for the entire lactation (re-drawn from Amos et al., 1985).



aReports on frequent milking or suckling during early lactation or on half-udders are represented in tables 3 and 5. bNumbers in columns represent the increase in milk yield observed with increased milking frequency. c 2X = twice daily milking; 3X = thrice daily milking; 4X = four times daily milking.

dDIM = days in milk

**Table 1.** Summary of selected literature reports on the effects of frequent milking (FM) on milk yield of dairy cowsa.

Importantly, the increase in milk yield in response to frequent milking or suckling is not specific to dairy cows; milk production was increased with frequent milking or suckling of other dairy ruminants, including goats (Wilde et al., 1986), sheep (Geenty & Davison, 1982; Negrao et al., 2001; Nudda et al., 2002), and buffalo (Dash et al., 1976), as well as various cross breeds (Little et al., 1991; Krohn, 2001; Sidibe-Anago et al., 2008; Alvarez-Rodriguez et al., 2010).

## **1.2. Effects of frequent milking or suckling on milk composition and cow health**

Reported effects of frequent milking on milk composition, somatic cell count (**SCC**) and herd health have been inconsistent. Many researchers have observed no effect of frequent milking on milk composition (Poole, 1982; Rao & Ludri, 1984; Amos et al., 1985; DePeters et al., 1985; Gisi et al., 1986), whereas some have observed a decrease in fat percentage (Allen et al., 1986; Smith et al., 2002). Due to the increase in milk production in response to frequent milking, however, there is often an increase in the total yield of fat and protein (Klei et al., 1997; Dahl et al., 2004b). With respect to SCC, some reports have indicated an association between frequent milking and decreased SCC, and these authors concluded that frequent milking may improve mammary health (Poole, 1982; Armstrong et al., 1985; Smith et al., 2002; Dahl et al., 2004b). Others have reported no effect of frequent milking on SCC (Waterman et al., 1983; DePeters et al., 1985; Gisi et al., 1986; Bar-Peled et al., 1995; Klei et al., 1997; Hale et al., 2003; Patton et al., 2006; Wall & McFadden, 2007a; Shields et al., 2011; Wright et al., 2011). The inconsistencies in the above reports may be the result of variations in timing and methods of sampling across experiments. Suckling of cows during early lactation has consistently been associated with a decrease in SCC and a decrease in the incidence of clinical mastitis, in some cases by up to 50% or more (Walsh, 1974; Edmunds, 1977; Little et al., 1991; Krohn, 2001). In fact, Walsh (1974) suggested that the increase in milk production elicited by suckling was probably due to the additional stimulus of the gland as well as the markedly improved mammary health of suckled animals.

Discrepancies also exist in the reported effects of frequent milking on reproductive performance and herd health. Some researchers have observed decreased reproductive performance in 3X cows compared to 2X cows (Ludwin, 1942; Armstrong et al., 1985; DePeters et al., 1985; Smith et al., 2002), whereas others have observed no effect (Poole, 1982; Amos et al., 1985; Gisi et al., 1986) or an improvement (Allen et al., 1986) in reproductive performance with 3X. Armstrong et al. (1985) suggested that any negative effects of frequent milking on herd health or reproductive performance may be associated with poor herd management. Well-controlled field studies using standardized sampling procedures will be necessary to verify the impact of milking frequency on milk composition, SCC and herd health, as well as identifying the interaction between frequent milking and herd management on these factors.

238 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

Klei et al., 1997 ≥ 1 Holstein Full lactation + 10.4% Smith et al., 2002 ≥ 1 Holstein Full lactation + 16%

2X = twice daily milking; 3X = thrice daily milking; 4X = four times daily milking.

c

dDIM = days in milk

dairy cowsa.

al., 2010).

animals.

**Reference Parity Breed Duration of FM Change in milk** 

bNumbers in columns represent the increase in milk yield observed with increased milking frequency.

1 Jersey Full lactation + 6.3%

aReports on frequent milking or suckling during early lactation or on half-udders are represented in tables 3 and 5.

**Table 1.** Summary of selected literature reports on the effects of frequent milking (FM) on milk yield of

Importantly, the increase in milk yield in response to frequent milking or suckling is not specific to dairy cows; milk production was increased with frequent milking or suckling of other dairy ruminants, including goats (Wilde et al., 1986), sheep (Geenty & Davison, 1982; Negrao et al., 2001; Nudda et al., 2002), and buffalo (Dash et al., 1976), as well as various cross breeds (Little et al., 1991; Krohn, 2001; Sidibe-Anago et al., 2008; Alvarez-Rodriguez et

**1.2. Effects of frequent milking or suckling on milk composition and cow health** 

Reported effects of frequent milking on milk composition, somatic cell count (**SCC**) and herd health have been inconsistent. Many researchers have observed no effect of frequent milking on milk composition (Poole, 1982; Rao & Ludri, 1984; Amos et al., 1985; DePeters et al., 1985; Gisi et al., 1986), whereas some have observed a decrease in fat percentage (Allen et al., 1986; Smith et al., 2002). Due to the increase in milk production in response to frequent milking, however, there is often an increase in the total yield of fat and protein (Klei et al., 1997; Dahl et al., 2004b). With respect to SCC, some reports have indicated an association between frequent milking and decreased SCC, and these authors concluded that frequent milking may improve mammary health (Poole, 1982; Armstrong et al., 1985; Smith et al., 2002; Dahl et al., 2004b). Others have reported no effect of frequent milking on SCC (Waterman et al., 1983; DePeters et al., 1985; Gisi et al., 1986; Bar-Peled et al., 1995; Klei et al., 1997; Hale et al., 2003; Patton et al., 2006; Wall & McFadden, 2007a; Shields et al., 2011; Wright et al., 2011). The inconsistencies in the above reports may be the result of variations in timing and methods of sampling across experiments. Suckling of cows during early lactation has consistently been associated with a decrease in SCC and a decrease in the incidence of clinical mastitis, in some cases by up to 50% or more (Walsh, 1974; Edmunds, 1977; Little et al., 1991; Krohn, 2001). In fact, Walsh (1974) suggested that the increase in milk production elicited by suckling was probably due to the additional stimulus of the gland as well as the markedly improved mammary health of suckled

Discrepancies also exist in the reported effects of frequent milking on reproductive performance and herd health. Some researchers have observed decreased reproductive

**yieldb (2X vs. 3Xc)** 

**Change in milk yield (2X vs. 4X)** 

> Similarly, suckling of a calf during early lactation of the cow is associated with increased weight loss and an increase in the days to first estrus (Margerison et al., 2002). In most cases, however, the delay in resumption of estrous cyclicity is offset by an increase in conception rate (Little et al., 1991; Krohn, 2001). Consequently, the effects of suckling on reproductive performance appear to be negligible, or in some cases positive (Table 2). In addition, Perez-Hernandez et al. (2002) reported that exposure of cows to a teaser bull decreased the effects of suckling on days to first estrus. Therefore, in agreement with the suggestion by Armstrong et al. (1985), simple changes in management - when feasible - can be used to overcome any potential negative impact of frequent milking or suckling regime on reproductive performance. Table 2 summarizes the findings of Little et al. (1991), who looked at lactation and reproductive performance of cows allowed to suckle calves for the first 90 days of lactation.


**Table 2.** Productivity characteristics of crossbred cows subjected to suckling compared to machinemilked herdmates. Cows were allowed to suckle their calves for the first 90d of lactation and were also machine milked twice daily for the entire lactation (Little et al., 1991).

In addition to the increase in milk yield, suckling during early lactation has also been associated with an increase in lactation length (Everitt & Phillips, 1971; Little et al., 1991; Krohn, 2001). This is particularly relevant since some producers are interested in incorporating an extended lactation management scheme into their herd. Extended lactation offers the benefit of decreased health risk to the cow because there is less exposure to risk of metabolic disease, which highest during the transition period. This, in turn, decreases costs to the producer associated with treating sick cows and veterinary expenses. The use of frequent milking or suckling offers a tool for increasing lactation persistency during extended lactations. Indeed, Sorensen et al. (2008) reported that the use of increased milking frequency makes an extended lactation cycle economically viable for the producer, in addition to an observed improvement in the health of the cow.

## **1.3. Effects of suckling on calf health and performance**

There are health benefits of keeping the calf with the cow and allowing the calf to suckle. Edmunds (1977) suggested that suckling calves generally perform better than those raised on milk replacer. Little et al. (1991) reported an increase in growth rate from birth to weaning of 0.2 kg/d for calves that were allowed to suckle vs. those that were raised on milk replacer. Similar observations were made by Alvarez-Rodríguez et al. (2010). In some cases, however, there is wide variation in the daily weight gain of suckling calves, especially if there are multiple calves on a single cow. Therefore, depending on the suckling scheme used, calves allowed to suckle don't always have higher growth rates than calves raised on milk replacer (Krohn, 2001). In a review of the literature, Edmunds (1977) reported that suckling calves had superior daily weight gain, a decrease in scours, and minimal incidence of other diseases compared to bucket-reared herdmates. The author suggested that this was a result of decreased stress associated with separation from the cow, since suckling calves are allowed almost constant contact with their mothers.

An interesting study conducted by Bar-Peled et al. (1997) reported on the performance of first lactation heifers that were allowed to suckle as calves, and compared them to heifers that were reared on milk replacer. Their findings are summarized in table 3, and have major implications regarding the effects of suckling on performance as adults; suckling clearly improved production efficiency in several areas.


**Table 3.** Productivity characteristics of heifers that were allowed to suckle as calves compared to herdmates raised on milk replacer. Heifers were allowed to suckle as calves for the first six weeks of life. Herdmates were raised on milk replacer (Bar-Peled et al., 1997).

## **1.4. The effect of parity on the response to frequent milking**

It has been reported that the milk production response to frequent milking was more pronounced in animals with smaller udder capacity, such as heifers (Woodward, 1931; Copeland, 1934; Lush & Shrode, 1953). Copeland (1934) speculated that this may be a function of increased udder pressure associated with less udder capacity. In agreement with this, Allen et al. (1986) observed that relative to 2X, 3X increased milk production by 13.4 and 19.4% in cows and heifers, respectively. In the previous year, however, another group reported that mature cows respond better to frequent milking than primiparous cows (DePeters et al., 1985). Of the studies that measured the milk yield response in heifers separately, most reported that heifers responded to frequent milking similarly to or better than multiparous cows. Therefore, no relationship has been established between parity and the magnitude of the milk yield response to frequent milking. To the contrary, we observed that that relative to multiparous cows, heifers respond similarly to increased milking frequency during early lactation (Wright et al., 2011). Similar observations have been made on the response of primi- vs. multi-parous cows to suckling during early lactation (Everitt & Phillips, 1971).

### **1.5. Economic impact of frequent milking or suckling**

240 Milk Production – An Up-to-Date Overview of Animal Nutrition, Management and Health

addition to an observed improvement in the health of the cow.

**1.3. Effects of suckling on calf health and performance** 

are allowed almost constant contact with their mothers.

life. Herdmates were raised on milk replacer (Bar-Peled et al., 1997).

**1.4. The effect of parity on the response to frequent milking** 

improved production efficiency in several areas.

extended lactations. Indeed, Sorensen et al. (2008) reported that the use of increased milking frequency makes an extended lactation cycle economically viable for the producer, in

There are health benefits of keeping the calf with the cow and allowing the calf to suckle. Edmunds (1977) suggested that suckling calves generally perform better than those raised on milk replacer. Little et al. (1991) reported an increase in growth rate from birth to weaning of 0.2 kg/d for calves that were allowed to suckle vs. those that were raised on milk replacer. Similar observations were made by Alvarez-Rodríguez et al. (2010). In some cases, however, there is wide variation in the daily weight gain of suckling calves, especially if there are multiple calves on a single cow. Therefore, depending on the suckling scheme used, calves allowed to suckle don't always have higher growth rates than calves raised on milk replacer (Krohn, 2001). In a review of the literature, Edmunds (1977) reported that suckling calves had superior daily weight gain, a decrease in scours, and minimal incidence of other diseases compared to bucket-reared herdmates. The author suggested that this was a result of decreased stress associated with separation from the cow, since suckling calves

An interesting study conducted by Bar-Peled et al. (1997) reported on the performance of first lactation heifers that were allowed to suckle as calves, and compared them to heifers that were reared on milk replacer. Their findings are summarized in table 3, and have major implications regarding the effects of suckling on performance as adults; suckling clearly

Body weight at conception (kg) 358.6 327.2 Average daily gain (kg) 0.82 0.68 Age at conception (d) 394 426 Conception rate (%) 83.4 74.2 Calving age (d) 669 700 Milk production (kg/300d) 9624 9171

**Table 3.** Productivity characteristics of heifers that were allowed to suckle as calves compared to herdmates raised on milk replacer. Heifers were allowed to suckle as calves for the first six weeks of

It has been reported that the milk production response to frequent milking was more pronounced in animals with smaller udder capacity, such as heifers (Woodward, 1931; Copeland, 1934; Lush & Shrode, 1953). Copeland (1934) speculated that this may be a

**Suckled Milk replacer**

Several research groups have characterized the economic impact of frequent milking. Factors contributing to the profitability of frequent milking were labor, herd size, herd health, management, feed costs, and milk price (Armstrong et al., 1985; Culotta & Schmidt, 1988; Maltz et al., 2003). Rao and Ludri (1984) reported that 3X increased net income by 21% relative to 2X. More recently, we estimated a net increase of approximately \$93/cow/yr when cows were milked 4X for the first 3 wk of lactation and milked 2X thereafter (Table 4; Wall & McFadden, 2007b). With respect to suckling, McKusick et al. (2001) estimated an increase in net income of \$25 per ewe/suckling lamb pair in a mixed rearing system (in which ewes are suckled *and* machine milked until lambs are weaned) relative to ewes solely machine milked and lambs raised on milk replacer. The increase in profitability of suckling management systems comes from eliminating the expenses associated with purchase of milk replacer, and also the increase in milk production of the dams after the suckling period. This, combined with the observation of Bar-Peled et al. (1997) that suckling calves perform better as adults, indicates multiple areas of economic gain with a suckling regime. Therefore, when there are no negative effects on animal health or reproductive performance, frequent milking or suckling has the potential to be a very profitable management tool.
