The average lactation yield and the fat and protein composition of milk for three dairy breeds are shown in the table below: | Breed | Milk Yield (kg) | Fat (%) | Protein (%) | |-------|------------------|---------|-------------| | A | 4350 | 5.3 | 4.1 | | B | 6450 | 4.1 | 3.5 | | C | 5240 | 4.8 | 3.9 | (i) Which breeds are represented by A, B, and C? (ii) Give a reason for your choice in each case - Leaving Cert Agricultural Science - Question 5 - 2016

A: The Jersey breed is known for its high fat content in milk, which corresponds to the 5.3% fat in the table.

B: Holsteins are the most common dairy cows, and their milk typically has a lower fat percentage, such as the 4.1% observed here.

C: The Frisian breed is recognized for its ability to produce a significant quantity of milk with a moderate fat content, aligning with the 4.8% fat.

The typical values for fat and protein in colostrum are:

• Fat: 14% to 16%
• Protein: The protein content can vary but is generally higher than in regular milk, often exceeding 4%.

The fat content of milk can be influenced by several factors, including:

1. Age of Cow: Older cows generally produce milk with higher fat content due to accumulated experience and modifications in metabolism.
2. Stage of Lactation: Fat content typically varies during lactation, being higher at the beginning and may decrease as lactation continues.
3. Health of Cow: Health issues can lead to fluctuations in milk composition, affecting fat levels. Healthy cows usually yield more consistent fat content.
4. Feed Composition: A higher quality feed, with adequate fiber and energy, can increase fat synthesis in milk, while poor feeding can lead to lower fat content.

The age and condition of breeding heifers significantly impact the date of first calving in the following ways:

• Age: Breeding heifers are typically around 15 months old at the time of calving. Heifers must reach a weight of around 500-580 kg to ensure a healthy calving process, which influences the timing.
• Condition: Heifers in optimal body condition (condition score of 2.8-3.2) are more likely to conceive and calve in a timely manner. Poor condition may result in irregular heat cycles or delayed calving.