**3. Bovine sex-biased milk production**

The main source of income in a dairy farm is, by far, milk sale and any factor that can increase or decrease the production affect significantly the farmers income. Even though external factors like feeding, rearing and management are an important part of profitability, other factors, intrinsic to animals can have an important impact on profitability of a farm. The genetic merit [40] and sex of the calf are some of those factors. Beside the intrinsic difference in the commercial value of a female or a male offspring in a commercial farm, if the female milk production is indeed affected by the calf gender, then it could be a major factor for maximizing profits [41].

**213**

advantage to the females.

*Calf-Sex Influence in Bovine Milk Production DOI: http://dx.doi.org/10.5772/intechopen.93966*

more male offspring [43, 44].

the value and widespread use of sexed semen [46].

lactation during its gestation or the lactation after their birth.

in the first lactation in French Holstein-Friesians [54] (**Table 1**).

Calf-sex biased milk production is the capability of a cow to adapt milk production and composition to the sex of her offspring, a phenomenon well documented in diverse mammalian species [19]. The milk yield and the quality of milk produced are two important characteristics in dairy cow production and are also of great impact in beef production. Any favoring of one sex over the other in bovine offspring can lead to a great increase in the use of sex sorted semen, despite its lower conception rate [42]. In dairy cows, birth sex-ratio is biased, with more males being born, which suggests underlying mechanisms operating to favor

Bull calves in dairy farms are mostly unwanted, due to their low value; in some countries, they are euthanized after birth, raising an ethical and social concern for the industry. On the other side, the used of sexed semen has higher costs and lower fertility. The fertility of sexed semen is estimated to be 8 to 17.9% lower in heifers compared to the conventional and not advisable to use in multiparous cows [42, 45, 46]. If a specific calf sex is associated with higher milk yield, this would have obvious consequences in

The growth rate of a suckling a male calf is higher than in females [47]. Therefore, it would be expected cows to have higher milk production or more energy dense milk when nursing a male. Despite differences in milk quantity or composition, cows do not show any sex biases in nursing behavior [29]. Since in most dairy farms, contrasting to most beef operations, calves are removed from the mother soon after calving, the pre and peri-natal mechanisms are the sole responsible for any observed milk-production sex-bias. Besides, cows are usually pregnant for most of the previous lactation [48], so the calf sex can potentially influence the previous

In *Bovidae*, data on the effect of calf sex in milk production are, to the least, inconsistent. Some studies reported an effect of calf sex on milk yield [1, 49–51], whereas other studies found no association [52]. One of the studies found that cows with a given genotype had higher milk yield in case of a male calf than a heifer calf [51]. In buffalos no effect between calf sex and milk production was reported [53]. In dairy cows in particular, studies addressing milk production sex-bias so far led to different results. While most studies described an advantage of female offspring, this effect was not observed for all the populations and a significant difference was not always observed [1, 33, 34, 40, 41, 54, 55]. Canadian and Iranian data for calf-sex bias in milk production found milk yield to be increased when a heifer was calved [41, 56]. However, a higher milk yield after calving a female offspring was only seen in the second lactation in New Zealand Holstein-Friesians [40], and only

However, Hinde et al. [1], with the largest study done so far on this topic, documented sex-biased milk production in US Holstein cattle. In his population, cows favor daughters, producing significantly more milk for daughters than for sons across lactation, suggesting that the effects of fetal sex can interact dynamically across parities. The sex of the fetus being gestated can enhance or diminish the production of milk during an established lactation. Moreover, the sex of the fetus gestated on the first parity has persistent consequences for milk synthesis on the subsequent parity. Contrastingly, Gillespie et al. [57] did not detect a significant effect of the sex of the calf being gestated on the mother milk production. Dallago et al. [55]. found only a calf-sex effect on the lactose and total solids, with an

On a population of 1.49 million cows from the late 90's, primiparous cows giving birth to a female produced, on average, additional 142 kg (1.3% increase) of milk over a standardized 305-day lactation period compared with those calving a male [1]. The fetal sex on the first parity had also persistent effects on milk production

### *Calf-Sex Influence in Bovine Milk Production DOI: http://dx.doi.org/10.5772/intechopen.93966*

*Animal Reproduction in Veterinary Medicine*

produce more progeny than weak sons [10].

to offspring gender, for example, by increasing milk production or changing its composition when she is nursing an offspring of the gender that has higher chances of producing future descendants. This strategy is particularly beneficial in species whose males compete for mating, like bovine, with dominant bulls leaving abundant offspring and weaker ones having no offspring at all. On the other side, this hypothesis also describes that investment in female offspring will be more profitable when the mothers are in poor condition because the chance of producing competitive male offspring is low. Well-nourished mothers invest more in male offspring, as strong sons will more likely leave more offspring, whereas even weaker daughters will

In agreement with this theory it has been shown that, in humans, the milk produced for males is more energy dense in well-nourished mothers [11], while mothers with low socioeconomic status, when nursing daughters produce milk with a higher fat content than when nursing sons [12]. However, evidence for systematic sex-biased favoring males has been equivocal [13–17]. Post-natal, sex-biased nursing care has been investigated as a possible reason for sex-biased milk production in several mammalians, including humans. Several studies reported evidence of sexbiased milk synthesis in different species but drawing definitive conclusions from

This chapter intents to discuss the evidences pro and against the existence of a sex-bias in cows´ milk production, by stressing the putative effects of the calf gender in consecutive lactations while focusing in particular in dairy cows. Albeit non-consensual, its existence would open new insights on the economic impacts of

In the last decades, industrial intensive milk production system uses the Holstein-Friesian breed, known as highest milk producing cow in the world. It is well documented that, with almost no exceptions, there has been a continuous increase in milk yield per cow. In all countries milk production and milk composition evolved over the years, due to a higher genetic merit and better management of the cows [31–32]. For example, from 2002 to 2013, in Denmark, all but two years showed a significant increase in the milk production compared to the previous year

[33]. In São Miguel island, Azores, the same evolution was observed [34].

the calf gender, then it could be a major factor for maximizing profits [41].

Also, in all countries, seasonal variations in milk production and composition were observed, both in intensive [35, 36] and pasture-based systems [37]. Previous studies have also proven that milk production varies with parity. It is generally observed a progressive increase in milk production in the first three to four parities

The main source of income in a dairy farm is, by far, milk sale and any factor that can increase or decrease the production affect significantly the farmers income. Even though external factors like feeding, rearing and management are an important part of profitability, other factors, intrinsic to animals can have an important impact on profitability of a farm. The genetic merit [40] and sex of the calf are some of those factors. Beside the intrinsic difference in the commercial value of a female or a male offspring in a commercial farm, if the female milk production is indeed affected by

these studies has been difficult for several reasons [11, 12, 18–30].

using sex sorted semen to enhance farm productivity.

**2. Evolution of dairy milk production**

and then a progressive decrease [38, 39].

**3. Bovine sex-biased milk production**

**212**

Calf-sex biased milk production is the capability of a cow to adapt milk production and composition to the sex of her offspring, a phenomenon well documented in diverse mammalian species [19]. The milk yield and the quality of milk produced are two important characteristics in dairy cow production and are also of great impact in beef production. Any favoring of one sex over the other in bovine offspring can lead to a great increase in the use of sex sorted semen, despite its lower conception rate [42]. In dairy cows, birth sex-ratio is biased, with more males being born, which suggests underlying mechanisms operating to favor more male offspring [43, 44].

Bull calves in dairy farms are mostly unwanted, due to their low value; in some countries, they are euthanized after birth, raising an ethical and social concern for the industry. On the other side, the used of sexed semen has higher costs and lower fertility. The fertility of sexed semen is estimated to be 8 to 17.9% lower in heifers compared to the conventional and not advisable to use in multiparous cows [42, 45, 46]. If a specific calf sex is associated with higher milk yield, this would have obvious consequences in the value and widespread use of sexed semen [46].

The growth rate of a suckling a male calf is higher than in females [47]. Therefore, it would be expected cows to have higher milk production or more energy dense milk when nursing a male. Despite differences in milk quantity or composition, cows do not show any sex biases in nursing behavior [29]. Since in most dairy farms, contrasting to most beef operations, calves are removed from the mother soon after calving, the pre and peri-natal mechanisms are the sole responsible for any observed milk-production sex-bias. Besides, cows are usually pregnant for most of the previous lactation [48], so the calf sex can potentially influence the previous lactation during its gestation or the lactation after their birth.

In *Bovidae*, data on the effect of calf sex in milk production are, to the least, inconsistent. Some studies reported an effect of calf sex on milk yield [1, 49–51], whereas other studies found no association [52]. One of the studies found that cows with a given genotype had higher milk yield in case of a male calf than a heifer calf [51]. In buffalos no effect between calf sex and milk production was reported [53].

In dairy cows in particular, studies addressing milk production sex-bias so far led to different results. While most studies described an advantage of female offspring, this effect was not observed for all the populations and a significant difference was not always observed [1, 33, 34, 40, 41, 54, 55]. Canadian and Iranian data for calf-sex bias in milk production found milk yield to be increased when a heifer was calved [41, 56]. However, a higher milk yield after calving a female offspring was only seen in the second lactation in New Zealand Holstein-Friesians [40], and only in the first lactation in French Holstein-Friesians [54] (**Table 1**).

However, Hinde et al. [1], with the largest study done so far on this topic, documented sex-biased milk production in US Holstein cattle. In his population, cows favor daughters, producing significantly more milk for daughters than for sons across lactation, suggesting that the effects of fetal sex can interact dynamically across parities. The sex of the fetus being gestated can enhance or diminish the production of milk during an established lactation. Moreover, the sex of the fetus gestated on the first parity has persistent consequences for milk synthesis on the subsequent parity. Contrastingly, Gillespie et al. [57] did not detect a significant effect of the sex of the calf being gestated on the mother milk production. Dallago et al. [55]. found only a calf-sex effect on the lactose and total solids, with an advantage to the females.

On a population of 1.49 million cows from the late 90's, primiparous cows giving birth to a female produced, on average, additional 142 kg (1.3% increase) of milk over a standardized 305-day lactation period compared with those calving a male [1]. The fetal sex on the first parity had also persistent effects on milk production


**215**

**Country**

New Zealand

UK Azores, Portugal

**Table 1.**

*Studies done so far to evaluate the effect of calf sex in Holstein cows' milk production.*

2009-2017

45,712

Holstein

2013-2014

211,932

Holstein

1995-2005

578,912

Holstein and Jersey

The lactation initiated by the birth of a female calf was associated with a 0.33–1.1% (p < 0.05) higher milk yield.

Female calf gender present carryover effects associated with higher milk yield in second lactations for Holstein Friesians (0.24%; p = 0.01) and third lactations for Jerseys (1.1%; p = 0.01).

Giving birth to a heifer calf conferred a 1% milk yield advantage in first lactation heifers, whilst giving birth to a bull calf conferred a 0.5% advantage in second lactation.

Whether calving a male or a female, cows roughly produced the same amount of milk and protein content. However, the content of fat was slightly higher when they calved females (P < 0.001).

[33]

**Years analyzed**

**N (lactations)**

**Breed**

**Main results**

**Study (chronologically)**

[39]

*Calf-Sex Influence in Bovine Milk Production DOI: http://dx.doi.org/10.5772/intechopen.93966*

> [46]


 *Studies done so far to evaluate the effect of calf sex in Holstein cows' milk production.*
