Nitrate Poisoning

Nitrate poisoning is due to a buildup of the compound in plants that cattle are grazing or accidental fertilizer ingestion. The nitrate ion in the plant becomes nitrite in the rumen, enters the blood stream and combines with red blood cells. This causes non oxygen carrying methemoglobin to form instead of hemoglobin. Cows are particularly vulnerable.

Clinical signs can occur within an hour of exposure to the toxic feed and include:

• Salivation and frothing

• Diarrhoea

• Abdominal pain (especially if fertilizer is the cause)

• Laboured breathing

• Staggered walking

• Body tremors

• Blue/grey gums

• Coma and death

Nitrate poisoning cases usually involve multiple animals. The treatment is methylene blue dissolved in saline given intravenously, which replaces methemoglobin with hemoglobin and if given quickly enough will save the animals life. While waiting for your vet to arrive, all animals that seem unaffected should be moved away from the toxic feed and monitored closely.

Eye fluid and blood from deceased animals can be tested for nitrate levels, and the blood usually has a characteristic chocolate brown colour.

Plants use nitrates for growth as a protein source, this process requires energy from photosynthesis. Nitrates build up in plants during periods where photosynthesis is limited such as during prolonged foggy weather, low temperatures and during frosts.

When rain breaks a drought, plants rapidly pick up nitrates and commonly become toxic.

The most affected feeds are annual rye-grasses, some new pastures, oats, kale, rape and brassicas. Suspect feeds can be tested either at your local Veterinary Centre clinic or test kits can be purchased for use on farm. The test turnaround time is approximately 40 minutes and only requires two handfuls of the feed. Toxic feeds should be retested at weekly intervals until safe to feed.

Risk can be managed by feeding suspect pastures or crops in the afternoon during winter, and filling cows up on hay before changing breaks.

Fodder Beet Feeding in Late Lactation

Feeding up to 5-6kg of Fodder Beet (FB) in late lactation has multiple benefits.

• It allows the round to be extended, with a relatively cheap supplement.

• Is very good for encouraging condition gain.

• Cows are partially transitioned before heading off farm for the winter.

Providing that there is still a significant quality grass portion in the diet (9 kg plus), it is unlikely that at 5-6kg/DM of FB that cows will be protein deprived. However, at 5-6kg of FB in the diet, a lactating cow still producing 1.7kg of MS will be in a negative balance for Calcium. She will be drawing on bone stores and have a higher chance of clinical milk fever. Calcium supplementation (~150g lime-flour cow/day) is important to maintain health and production, and reduce bone calcium exhaustion before the next lactation.

One problem that we repeatedly see with FB transition is the creation of space for cows to get onto the crop. Creating a headland in the crop by using a Beet bucket and feeding this in the paddock initially works very well. Once on a crop, a herd needs 1 linear metre/cow on the face and 6 square metres (minimum) of room/cow on the headland.

Cows should start on an allocation of not more than 1-2kg/cow/day. Maintain this for 3 days until all cows are eating and then increase by 1kg every second day. Cows are best to go onto the crop hungry to encourage shy eaters.

Using an ‘increasing time allocation technique’ and using a big, long break (6-7m2/cow) to enter a paddock can be risky. Those that use it usually start with 15 minutes (precisely!) and increase the time by 5 minutes every 3 days. Once a long headland is established (fully eaten), then move to using accurate measured daily allocations. Use a stop-watch and wait with the cows!

When setting an allocation, it is easiest to calculate if the fence is shifted parallel to the rows. Cows will graze 12-18 inches under the wire so will effectively always be eating the next row.

Train the cows to stay and eat their allocation. Even if most is eaten in 20 minutes, cows should stay on the break for 2-3 hours so they all learn that they need to eat.

Never allow beet to build up in a break. You have over allocated and need to pull back. Day 7-10 on crop is where problems often occur when cows will suddenly click and eat the accumulated surplus.

You must accurately measure your crop yield to enable accurate per cow allocation!

Small Changes for a Big Impact in Lameness Reduction

Daily lame cow numbers aren’t quite up there with Omicron cases, but they’re certainly not reducing. With the nature of the weather this year, neither the cows, nor farm staff, are getting a break when it comes to lameness. While the weather has played a large part in the increased numbers, lameness is of course multifactorial. It is hard during the milking season to make infrastructure changes to tracks, so remembering the impact humans have on lameness is important in keeping numbers as low as possible even with other on-going issues:

1. Walking distances – older, heavier cows should ideally be walking the least distance on the farm. With many people on 16 hourly or similar the distance cows are walking is already reduced, but still consider trying to keep at risk cows in paddocks closer to the shed. As ever, cows in a lame mob should be as close as possible.

2. Standing times – starting milking as soon as is practically possible after cows have been collected is a good tool in reducing lameness. Decreased pressure on feet means smaller chance of white line separation and subsequent lameness

3. Feed management – do lame cows go skinny or do skinny cows go lame? This could be an article in itself. Keeping cows in good body condition will maintain a good fat pad in the foot which protects the bone in the foot from damage and lameness

4. Pushing cows – maintaining distance and bringing cows in at a relaxed pace will allow the cows to be a bit more selective on where they walk on deteriorating tracks. Cows will naturally slow down walking on poor tracks so allowing a bit more time than normal when bringing in cows and not getting frustrated at a slower pace could save a case or two of lameness every day.

5. Cow flow – hopefully at this stage in the season cow flow in and out of the shed should be good. Keep top gate use to a minimum or not at all. Backing gate shouldn’t be used in the first 20 minutes of milking and should either be set on a timer thereafter or moved a small amount after a certain number of cows have been milked. The backing gate should only ever be used to close space on a yard – never to physically move cows.

6. Collecting yard – make sure the collecting yard is properly hosed down after each milking and ready for the next. Lots of stones are being brought on to yards just now and getting rid of them is a huge help in reducing lameness.

7. Treatment –early, effective treatment of lame cows is still the most powerful tool in helping reduce future lameness. Using blocks or cow slips gives the damaged hoof chance for repair. Administering an anti-inflammatory (such as ketomax) will help decrease chances of permanent change within the hoof and also provide pain relief to lame cows.

Lameness in a season like this can certainly be overwhelming and it’s a depressing sight to see big numbers in the lame cow mob. If you need help with treating cows, please don’t hesitate to ring us.

Correctly Identifying the Lame Claw

Over the years I have witnessed multiple occasions where farm staff have attacked hooves with knives, grinders and hoof trimmers before correctly determining the site of lameness. This will have frequently resulted in an exacerbation of the overall lameness in the cow.

Before putting any lame cows into the crush, it is important to determine which leg is affected. Our vets tend to record these on a recording sheet. Look for:

• obvious swelling (and hoof shape)

• weight bearing while standing still (the lame foot will be positioned so not to carry as much load)

• a head nod while walking in the case of front leg lameness

• the stride length and speed (the lame leg will have a short stride before taking weight, then the sound leg swings through with a longer stride and is weight loaded for longer.

Once you have determined the lame leg, have tied it up, washed it down and checked for footrot, use hoof testers to confirm where the lameness is located. This simple tool works by squeezing and putting pressure on the claw. Watch for a repeatable pain response which is easy to recognise in the hind legs by a tensing of the ‘hamstring’ muscles and the front legs by a tensing of the shoulders. Cows with sole bruising will often have very soft hooves and you will see that the testers easily depress the sole. If there is no response to either claw to hoof testers, then chances are you either have the wrong foot or the cause of lameness is located further up the leg.

Yersinia in Calves

In December we start to see outbreaks of Yersinia in weaned calves, typically from post-weaning through to about May. Yersinia bacteria are found in the intestines of most calves – 85% of herds (calves) have Yersinia as a normal gut resident. Stress/immunosuppression associated with parasites, nutrition, trace element deficiencies and BVD may result in an overgrowth of this bug in the intestines. Overgrowth results in a severe scour. Because of a constantly irritated bowel, faeces are often seen dribbling down on to the back legs.

As infection spreads, so does infection pressure and faecal-oral transmission then occurs. Large percentages of a mob are often affected severely checking growth rates. Mortality rates of 5-10% are not uncommon. Faecal culture confirms the diagnosis; however, a presumptive diagnosis can often be made on history and clinical signs. Isolation of affected animals to reduce the spread and treatment with oxytetracycline antibiotic for 3-5 days is an effective treatment/control.