NZ Dairy Heifers: snapshot of weight and milk production
Updated: Jun 12, 2020
Based on the latest Dairy Statistics, the most common breeds of dairy cattle in New Zealand are Friesian (33.1%) and Jersey (8.6%). Interestingly, the most common breed category is Friesian-Jersey crossbred, at 48.5% of NZ cows.
The majority of studies split animals into 3 breed categories: Friesian, Jersey and Friesian-Jersey crossbred. However, within the Friesian-Jersey crossbred category, animals can vary greatly in how much Friesian and Jersey proportions they contain.
We know from many previous studies that there are big differences between Friesians and Jerseys in terms of their live weight and milk production.
This week's post is the first of multiple posts based on a journal article that aimed to investigate the relationships between weight and milk production of dairy heifers.
This post summarises the average weights and milk production of dairy heifers that were classified into 5 breed categories ranging from more to less Friesian;
Holstein-Friesian crossbred (FX)
Holstein-Friesian-Jersey crossbred (FJ).
Jersey crossbred (JX)
Of the 5 breed groups studied, Holstein-Friesian crossbreds (FX) was the largest group with 33% of heifers.
As heifers became older, and as heifers became less Jersey and more Holstein-Friesian, they became heavier.
Holstein-Friesian crossbred (FX) and Holstein-Friesian-Jersey crossbreds (FJ) produced more milk solids than Jersey (J), Holstein-Friesian (F) or Jersey crossbred (JX) heifers.
This summary is part of a series - for Part 2 have a read here: Do heavier heifers produce more milk?
For those of you that are familiar with breed 16ths the breakdown of how the heifers were classified into each of the 5 breed groups is in the table below.
For those of us that are not familiar with breeds expressed as 16ths here is the "Plain English" description as well.
There were nearly 190,000 heifers used in this study, the largest breed group was FX with 33% of heifers.
Ages studied were 3, 6, 9, 12, 15, 18 and 21 months of age within each of the 5 breed groups.
As expected, average weights increased with age (Figure 1).
Further, for each age, as heifers became less Jersey and more Holstein-Friesian, they became heavier.
The table of weights provide good benchmark data for average heifers in NZ.
FJ heifers were approximately 150 kg at six months of age, 300 kg by 15 months of age and by 21 months of age they were approximately 420 kg.
Although not shown in the figure above, the range in weights observed for each breed group was fairly large, showing that even when crossbreed heifers are split into groups based on being more or less Jersey or Friesian, there was still considerable variation in how heavy they were.
Milk production in first lactation was known and was compared among the 5 breed groups.
Milk solids production - measured as milk fat + milk protein, was highest for FJ (grey) and FX (purple and white stripe) heifers (Figure 2).
F heifers (purple) had the second highest milk production at 301.6 kgMS and J heifers (blue) had the lowest milk production at 286.1 kgMS in first lactation (Figure 2).
The letters (a,b,c,d) at the bottom of Figure 2 above (and the other figures in this post) are used to show where the breed groups are different.
If 2 breed groups have the same letter (e.g. both FJ and FX have a letter 'a') this means that 'statistically they are no different'. If they have different letters (e.g. FJ has an 'a' and JX has a 'c') this means that 'statistically they are different'.
Accumulated three-year yields
Next up we looked at their accumulated yield. Now ideally, we would have studied 'lifetime yields' which would be their total milk production from their first calving up until they exited the herd.
Unfortunately, we didn't have that information for all heifers. We settled for an in-between measure: 'Accumulated three-year production'.
This is the total milk production for 3 years (or dairy seasons) from their first calving. Or in other words their 'lifetime' yield up until the end of their 3rd lactation.
For the super successful heifers that calved each of these 3 years, their accumulated yield was the sum of their first + second + third lactations.
For the less successful heifers that only had 2 calvings, their accumulated yield was the sum of their first + second lactations.
The unsuccessful heifers that only had 1 lactation, their accumulated yield was considered as their first lactation milk yield.
The average 3-year accumulated milk solids production was highest for FJ and FX heifers at 817 and 813 kgMS, respectively (Figure 3).
Both JX and F heifers had similar accumulated 3-year milk solids yields to each other at 792 kgMS for JX and 783 kgMS for F heifers (Figure 3).
J heifers had the lowest 3-year accumulated milk solids production at 735 kgMS (Figure 3).
Now you may be thinking that these accumulated yields are lower than what we would expect based on their first lactation production - you would be correct!
As mentioned before, some heifers only had 1 or 2 lactations worth of milk production to contribute to their accumulated yields. The dataset used for this study had approximately 19% of heifers with only their 1st lactation, 15% with their 1st and 2nd lactations and the remaining 66% had all 3 lactations worth of data.
It is due to these 19% and 15% of heifers that the average accumulated yields are lower than what we might expect based on the sum of 1st + 2nd + 3rd lactations.
Including heifers that did not complete all 3 lactations is better at describing the effects on accumulated milk production without being picky about whether that increased milk came from greater production per cow or from greater survival of said cow.
All heifers incur the costs of rearing, the heifers that only complete 1 or 2 lactations are not contributing as much milk to the vat despite having incurred all the costs of rearing. Therefore, all heifers that were old enough and should have had 3 lactations were included (regardless of whether they actually had 1, 2 or 3) to allow a good indication of the milk production response if a farmer were to invest in their heifer rearing practices.
These average live weights and milk production for the 5 breed groups provide excellent baseline data for NZ dairy heifers.
The second part of this journal publication was to analyse the relationship between weight and milk production for each breed group. This was done to understand whether heavier heifers produce more milk and whether there are 'optimum' weights that we should be striving to achieve in order to get the best performance from dairy heifers, dependent on their breed makeup.
As this weeks post is long enough, we have summarised the second part here: Do heavier heifers produce more milk?
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Handcock RC, Lopez-Villalobos N, McNaughton LR, Back PJ, Edwards GR, Hickson RE. 2019. Positive relationships between body weight of dairy heifers and their first-lactation and accumulated three-parity lactation production. Journal of Dairy Science. 102(5):4577-4589.