[MUSIC] Hello. My name is Troy Ott, and I'm a professor of Reproductive Biology in the Department of Animal Science at Penn State. My research focuses on factors affecting fertility in dairy cows, and I teach reproduction to undergraduate and graduate students. Before we begin to talk about reproduction in a dairy cow, it is important that we take a moment to look at the big picture. What is it that we want for these beautiful and gentle animals as they help us feed a hungry world? Well, first and foremost, we want to create environments that maximize the welfare and comfort of cows on our farms. Cows that are not comfortable do not produce milk well and end up costing dairy producers money. Second, we want to produce a wholesome, nutritious product that people can afford. To achieve these goals, we like to think about the optimal life cycle of the dairy cow in our herd. An easy starting point is birth, or calving. We want to make sure that calves are born into a comfortable and sanitary environment. And that they consume high quality Colostrum with in their first 3 hours of life. Now colostrum feeding will be covered in another section. But just as a reminder, colostrum is the first milk the cow produces for her calf that is rich in antibodies. It is these antibodies that will protect the calf from disease during the weeks and months of life, while it's own immune system develops. Remember, regular milk or milk replacer are poor substitutes for high quality colostrum and will not protect your calves from disease. Modern production systems use an immediate or early weaning process where the calf is removed from the mother shortly after nursing colostrum or immediate if high quality colostrum is provided by a bottle or two. This is done to reduce stress on the calf and the mother. Now you may think that this seems odd that early removal of the calf reduces stress, but it does. Imagine if we leave the calf on the cow for days or weeks and then separate them, this would be a great stress to the calf and to its mother. Once the calf is removed, it can be individually cared for, and it is not at rick for injury or disease from mixing with older cows. This newborn calf then enters the equivalent of elementary school where it is grouped together with other calves of similar age in pens, and transitioned over several months from a diet of mil or milk replacer, on to solid feed. During this time, it is important that the calf receive all the necessary vaccinations to ensure that it will be ready to fight disease. These vaccinations vary by location and country, and you should consult with your veterinarian as to what is recommended in your area. Attempting to save money by skipping needed vaccinations is risky and will likely result in large losses later. Remember, these dairy heifers are the future of your herd and they should be treated with the utmost care and attention. Now, when is your young dairy heifer ready to take her spot in the milking herd? Well, this can vary a bit by breed and production system. But I will provide a few key pointers to make sure this first big step in her productive life is a good one. Before a heifer will lactate or produce milk, she must reach puberty. Now you're not going to need to worry about acne or who she will be taking to her high school dance like humans. But achieving puberty at the right time is important for profitable dairy production. The main goal here is that the dairy heifer is fed an appropriate diet to allow her to achieve puberty consistent with cows of her breed. How to achieve this will be covered in detail elsewhere in the course. We can define puberty in animals in several ways, but for dairy cow we define puberty as the age which she can carry a healthy calf to term with compromising her health. This means that even though some cows may achieve puberty and start their reproductive cycles at an early age, we need to wait until that heifer achieves the appropriate size and weight before we breed her. Interestingly, it is a heifer's weight and skeletal size. Now, her age, that has the largest affect on, the age at which she achieves puberty. When evaluating heifer's to breed, we need to look at both the skeletal size which, we typically measure by withers height, or the height at her shoulder and weight. As a general rule, a hosting heifer will start cycling when she achieves about 50 to 55% of her mature body weight. But she will need to reach roughly two thirds of her mature body weight before she should be bred. In addition, modern Holsteins should be 48-50 inches to be considered adequately grown for breeding. Frame size and weight are better measures of the physiological age of the heifers. If we only use age as a parameter for breeding, some heifers may be too small, and others too large. Finally, it should be clearly understood that nutritional status drives reproductive cyclicity and fertility. So if your not feeding your animals well, they will achieve puberty late and will have reduced lifetime productivity. Likewise, if you over feed the heifers, they will also have problems with fertility. In general, our goal is for Holstein to calf and begin their lactation between 22 and 24 months of age. Of course this is somewhat breed dependant, but it is a good rule of thumb. Now, a heifer calving for the first time is an animal that should receive careful attention. First of all, she has been in your herd for two years, and has not generated any income. If something goes wrong at this stage, it is very expensive for the dairy producer. Second, although we look forward to each calf the cow gives us, calving is the most dangerous time in a cow's life and getting your cow successfully through this transition period is the key to profitable dairy production. Once she is calved a two year old heifer must be managed to deal with the nutritional challenges of high milk production and also to support body growth which should continue through the next year. Now that we have gotten the heifer to reproductive age it is important that we take some time to understand basic reproductive anatomy and hormonal control of reproductive simplicity. Both of these are important for effective management of reproduction in your dairy herd, for example If you practice artificial insemination or even use bulls to inseminate your cows, understanding how to manage insemination is critical for success. Furthermore, if you plan on using technologies to synchronize your cow herd, you must have an understanding of how hormones affect their reproductive processes. These topics will be covered in the next lecture. To summarize, managing the calving process is key to the success of a dairy operation. Calves should be provided with high quality colostrum and receive adequate vaccinations at the correct times during early life. It is important to remember that cows may start to cycle before they are of adequate size to conceive and carry a pregnancy successfully to term. Remember to focus on body size and weight, not just age, when making breeding decisions. Cows should achieve two thirds of their mature body weight, and have adequate skeletal size before breeding. The ultimate goal is to have the heifer calf for the first time between 22 and 24 months of age at adequate body size and weight to support the demands of continued growth and lactation. [MUSIC]