Pregnancy The Final Goal
Dry cow, springer cow and fresh cow nutrition will have influence on our next twelve months viability, outside milk price; but pregnancy will be the real determining factor. Timely return to pregnancy will be influenced most by all the proceeding management activities associated with transition; and my definition of transition is from dry-off to pregnancy tested, in-calf!
Of the financial indicators for profitable dairy farming, fertility ranks equal first with feed intake. And there is a correlation between the two, but both heavily influenced by transition management. It is important to start with the end goal in mind to drive our prior management efforts toward that goal. From the goal of timely return to pregnancy, we’ll work backwards to dry-off as each preceding management activity will influence the following one.
Immunity and reproduction work in tandem for achieving our goal. David Hurley, a researcher at the University of Georgia USA sights data showing the average dairy cow in the USA does not last more than two lactations. Although we in Australia might scoff at this, ‘carry-over cows’ are generally not tolerated, as close scrutiny of economic factors in profitable dairy businesses highlight their drain on farm profits. Hurley states, “Problems with mastitis or pregnancy are leading reasons for culling cows. Inflammation (and it is systemic – italics mine) associated with mastitis has been associated with failure to establish pregnancy”.
Establishing a strong immune system is essential, but management factors we have control over are also equally essential to prevent infections of any kind that draw an immune response causing systemic inflammation that is so damaging to fertility. Immunity and reproduction are intimately connected in both positive and negative ways. Bacterial colonisation in the lower reproductive tract is normal and the immune response to clean up this also helps to regenerate new cells of the uterine lining. This creates a conducive environment for conception and foetus attachment to the uterine wall.
However, immune response to fight other infections can cause inflammation in the reproductive tract and alter interaction between sperm and egg. Some immune responses interfere with corpus luteum development disrupting normal cycle. Uterine mucus can be changed in viscosity, physical and chemical composition reducing sperm penetration and damaging membranes reducing sperm fertilisation capacity. Immune response-inflammation from sites not actually connected to the uterine environment, for example, mastitis, respirator or hoof infection. These same altered uterine conditions can also impede fertilised ovum from implanting in the uterine wall resulting in early embryonic death.
A strong immune system is obviously essential. Feeding adequate energy and protein are critical to immune efficiency. Immune function is a very energy-hungry system and most at risk immediately post-calving when competing with rapidly rising milk production and mammary system demand for energy. Unfortunately, immediately post-calving is also the highest risk time for our cow in regard to infection and immune defences. Apart from nutrition, developing a sound vaccination program in conjunction with your veterinarian can assist in building the adaptive immune system, enabling our cow to deal with invasion without clinical disease consequences and minimise inflammatory effects on fertility.
Preventing infection
Mastitis is now well known to interfere with fertility due to systemic inflammation created by defence mediators sent out to address the infection. A high portion of mastitis cases occurs in fresh cows from both sub-clinical infections prior to dry-off, and environmental exposure around calving as pressure in the udder forces leakage of milk opening teat ends and allowing pathogen entry. Many farms report improvement in reduced mastitis around calving through administering Dry Cow therapy and Teat Seal.
Uterine infection comes under the nutrition heading. Initially, from lack of mineral nutrition (trace minerals especially) during the previous lactation, but not eliminating minerals during both the dry and springer periods. Trace minerals, particularly selenium, play a major role in release of placental membrane, but calcium is also a significant player. Calcium is a critical element in sound immunity too.
Energy and protein have major roles in the symphony of the physical, metabolic and hormonal crescendo of giving birth. When one of these elements is deficient during late gestation, birth and immediate post-calving, the process from there on is often described as a cascade of metabolic disease – milk fever, ketosis, metritis, mastitis. They all precipitate one and another.
We started this series of articles last month with the dry cow phase, which, arguably, is the most neglected phase of the dairy cow’s annual cycle. The traditional transition phase of twenty one days prior to calving to twenty one days post-calving has held centre-stage for research funds and effort for many years, with major improvement in cow health, production and lifespan. The dry phase was assumed to have little influence provided the cow stayed in reasonable shape. The shift in recent years, due to some niggling problems in fresh cows that were not responding to transition par excellence, has sent researchers scurrying to study dry cows. This opened a ‘Pandora’s Box’ of causes to not just those niggling problems, but to other seemingly unrelated post-calving issues, none more important than fertility.
Managing energy, protein and mineral nutrition right through my extended transition definition (dry-off to confirmed pregnancy) is paramount to good fertility which translates to farm business profit. Any changes in live-weight during pre-calving will precipitate ketosis either clinical or sub-clinical. This then manifests into reduced feed intake post-calving and weight loss which in turn virtually negates conception, if not cycling. The unborn calf is fed protein via the umbilical cord. A protein deficient diet pre-calving will encourage energy consumed by the dry cow to be converted to protein by the cow reducing both energy and protein for her own maintenance. The result is ketosis post-calving, and possible before calving as our own blood test research on dry cows, springers and fresh cows has shown. Protein deficiency, especially in the springing cow ration, will reduce colostrum immunoglobulin content significantly.
Calcium is a subject I want to address separately in a future article, but suffice to say, apart from direct implications to milk fever, clinical or sub-clinical; its deficiency has major negative effects on fertility. This is especially true in our pasture based systems that are inherently low in calcium by comparison to Northern Hemisphere diets containing Lucerne: a powerful argument for the return of clover to our pastures.
John Lyne is a dairy production specialist with Dairytech Nutrition
www.dairytechnutrition.com.au
