**7. The use of sexed semen**

Sexed semen produces 90% of offspring of the desired sex, but the fertility is reduced in between 75 to 80% compared with conventional frozen semen [117], because the sorting process produces a higher level of damaged to the spermatozoa [118]. Usually, sexed semen is applied more frequently in heifers, to profit from their higher fertility. Also, the heifers selected to be inseminated with sexed semen are usually the ones with higher genetic merit, so they are the ones producing the replacement animals [66].

The use of sorted semen in dairy industry screws the gender ratios into the female sex, seeking the production of future genetically superior replacement animals. Under the sex-biased milk production framework, and according to some studies [1, 41, 57], it would be expected to observe an increase in milk yield in cows that calved a female in their first and eventually in the second parity. This effect would overcome any negative effects exerted by the calving of a larger male fetus (increasing the stress over nutrients partitioning between the fetus and the mother during pregnancy, and increasing the risk for dystocia) and variations in pregnancy length. On the other hand, the sorted semen being applied more often in heifers or primiparous cows, the former tending to present shorter pregnancy lengths [76], may also influence the results if the type of semen used does not enter in the model used. Attention should be paid when analyzing data from most studies, because usually the type of semen used in artificial insemination is not considered as a variable in the statistical model, which could affect the results.

After investigating the effect of sex-bias in milk production, using simulated data and considering different intensities of sexed semen in three different scenarios, two studies concluded that including sex-bias could increase profitability between €4.0 and €9.9 per cow per year [58, 119] (**Table 3**). On the other hand, it was also concluded that any increase in milk yield from cows calving a female calf was insufficient to warrant the use of sexed semen. The real influence of sex-biased milk production using sexed semen must be further studied before recommendations can be made into its economic impact [40]. Also, two different studies concluded that, even though there might be an effect of calf gender on a cows' milk production, the

**223**

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

> **Without sex bias**

**Differences in milk yield** 

**per cow/year**

semen [56].

**Table 3.**

observed.

understood.

**Acknowledgements**

**Conflict of interest**

**8. Conclusions**

impact was not large enough to influence profit [54] or encourage the use of sexed

*Effects of the use of sex sorted semen on milk yield per cow/year considering two different simulation scenarios [109].*

**With sex bias**

Milk yield (kg of ECM) 36 48 Sorted semen used in 30% of heifers and

Milk yield (kg of ECM) 66 99 Sorted semen used in 100% of heifers and

30% of cows Net return (€) 3.0 7.0

50% of cows Net return (€) 3.1 13.0

**Simulation scenario**

Whether or not a sex biased milk production in dairy cows exists, this bias can vary, favoring one sex or the other and, sometimes, none. It seems to favor females in intensive production systems, while in other less intensive systems this was not

The conflictual results obtained in different studies considering the cow may influence the sex of offspring suggest that the systems were cows are generally in good and competitive condition produce more milk for bull calves. They also seem to indicate that cows in a worse condition, or of a genetically diverging strain, apparently invest more milk in heifer calves. Up to now, conflicting reports have been presented to the scientific society, but differences among the models used make difficult to establish a clear relation between the gender of the offspring and the productivity of the cow. The different results observed are probably due to differences in the methodological approach, and the different influencer parameters used to calculate a lactation milk production, and in possible confounding factors that may not be completely identified. Also, other factors, such as different housing and feedings can have impact in calf-sex milk production bias in pathways still to be

To further explore this theory, additional research is needed that includes other cattle populations and correlating the investment strategy with an animal welfare index. If the calf sex effect in milk production is present in a population, selection of bull mothers and progeny tested bulls may be biased due to the offspring sex, increasing the genetic progress towards more profitable cows, if this calf-gender

This work was funded by the project UIDB/CVT/00772/2020, supported by the

bias is accounted for in breeding value estimation.

Portuguese Science and Technology Foundation (FCT).

The authors declare no conflict of interest.

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


**Table 3.**

*Animal Reproduction in Veterinary Medicine*

pregnant at peak lactation [109].

studied yet.

impact [40].

**7. The use of sexed semen**

replacement animals [66].

The sex of the calf whose birth initiates lactation can influence the milk production in the subsequent lactation because of the hormonal influences on the mammary gland development or due to the calf sex effects on pregnancy length. Also, fetal sex can influence lactation production during pregnancy because cows become

In the *Cervus elaphus* species, the red reindeer, dominant females give birth to a higher proportion of males than their subordinates. It is known that these dominant hinds produce higher levels of progesterone in the early days of pregnancy, and male blastocysts secrete interferon-tau earlier than females, so the hypothesis is that maternal recognition of pregnancy in dominant hinds is therefore more likely to be successful if the blastocyst is male [116]. Factors such as this at the time of maternal recognition of pregnancy in cattle could also affect calf sex, but this has not been

Holstein heifers in the USA, even after administration of bST (bovine somatotropin) still produced significantly higher milk yield if they calve a female offspring, but sex-biased milk synthesis was not observed in parities two through five [1]. Even though hormones can cause sex-biased milk production, other factors such as birth, weight, lactation length and dystocia probably have a higher

Sexed semen produces 90% of offspring of the desired sex, but the fertility is reduced in between 75 to 80% compared with conventional frozen semen [117], because the sorting process produces a higher level of damaged to the spermatozoa [118]. Usually, sexed semen is applied more frequently in heifers, to profit from their higher fertility. Also, the heifers selected to be inseminated with sexed semen are usually the ones with higher genetic merit, so they are the ones producing the

The use of sorted semen in dairy industry screws the gender ratios into the female sex, seeking the production of future genetically superior replacement animals. Under the sex-biased milk production framework, and according to some studies [1, 41, 57], it would be expected to observe an increase in milk yield in cows that calved a female in their first and eventually in the second parity. This effect would overcome any negative effects exerted by the calving of a larger male fetus (increasing the stress over nutrients partitioning between the fetus and the mother during pregnancy, and increasing the risk for dystocia) and variations in pregnancy length. On the other hand, the sorted semen being applied more often in heifers or primiparous cows, the former tending to present shorter pregnancy lengths [76], may also influence the results if the type of semen used does not enter in the model used. Attention should be paid when analyzing data from most studies, because usually the type of semen used in artificial insemination is not considered as a variable in the statistical model, which could affect the results.

After investigating the effect of sex-bias in milk production, using simulated data

and considering different intensities of sexed semen in three different scenarios, two studies concluded that including sex-bias could increase profitability between €4.0 and €9.9 per cow per year [58, 119] (**Table 3**). On the other hand, it was also concluded that any increase in milk yield from cows calving a female calf was insufficient to warrant the use of sexed semen. The real influence of sex-biased milk production using sexed semen must be further studied before recommendations can be made into its economic impact [40]. Also, two different studies concluded that, even though there might be an effect of calf gender on a cows' milk production, the

**222**

*Effects of the use of sex sorted semen on milk yield per cow/year considering two different simulation scenarios [109].*

impact was not large enough to influence profit [54] or encourage the use of sexed semen [56].
